I'm not quite sure that this is appropriate for YOUmoz, but I am sure that it's useful information for newcomers to this community. I have no doubt that there will be some disagreement about some of these definitions, because some of them are probably wrong, and comments about errors and omissions are more than welcome.

A-B-C-D-E-F-G-H-I-K-L-M-N-O-P-R-S-T-U-W

301 A permanent server redirect - a change of address for a web page found in the htaccess file on apache servers. Also useful for dealing with canonical issues.

adwords Google Pay Per Click contextual advertisement program, very common way of basic website advertisement.

adwords site (MFA) Made For Google Adsense Advertisements - websites that are designed from the ground up as a venue for GA advertisements. This is usually, but not always a bad thing. TV programming is usually Made For Advertisement.

affiliate An affiliate site markets products or services that are actually sold by another website or business in exchange for fees or commissions.

algorithm (algo) A program used by search engines to determine what pages to suggest for a given search query.

alt text A description of a graphic, which usually isn’t displayed to the end user, unless the graphic is undeliverable, or a browser is used that doesn’t display graphics. Alt text is important because search engines can’t tell one picture from another. Alt text is the one place where it is acceptable for the spider to get different content than the human user, but only because the alt text is accessible to the user, and when properly used is an accurate description of the associated picture. Special web browsers for visually challenged people rely on the alt text to make the content of graphics accessible to the users.

analytics A program which assists in gathering and analyzing data about website usage. Google analytics is a feature rich, popular, free analytics program.

anchor text The user visible text of a link. Search engines use anchor text to indicate the relevancy of the referring site and of the link to the content on the landing page. Ideally all three will share some keywords in common.

astroturfing (the opposite of full disclosure) attempting to advance a commercial or political agenda while pretending to be an impartial grassroots participant in a social group. Participating in a user forum with the secret purpose of branding, customer recruitment, or public relations.

authority (trust, link juice, Google juice) The amount of trust that a site is credited with for a particular search query. Authority/trust is derived from related incoming links from other trusted sites.

authority site A website which has many incoming links from other related expert/hub sites. Because of this simultaneous citation from trusted hubs an authority site usually has high trust, pagerank, and search results placement. Wikipedia, is an example of an authority site.

B2B Business to Business.

B2C Business to Consumer

back link (inlink, incoming link) Any link into a page or site from any other page or site.

black hat Search engine optimization tactics that are counter to best practices such as the Google Webmaster Guidelines.

blog A website which presents content in a more or less chronological series. Content may or may not be time sensitive. Most blogs us a Content Management System such as WordPress rather than individually crafted WebPages. Because of this, the Blogger can chose to concentrate on content creation instead of arcane code.

bot (robot, spider, crawler) A program which performs a task more or less autonomously. Search engines use bots to find and add web pages to their search indexes. Spammers often use bots to “scrape” content for the purpose of plagiarizing it for exploitation by the Spammer.

bounce rate The percentage of users who enter a site and then leave it without viewing any other pages.

bread crumbs Web site navigation in a horizontal bar above the main content which helps the user to understand where they are on the site and how to get back to the root areas.

canonical issues (duplicate content) canon = legitimate or official version - It is often nearly impossible to avoid duplicate content, especially with CMSs like Wordpress, but also due to the fact that www.site.com, site.com, and www.site.com/index.htm are supposedly seen as dupes by the SEs - although it’s a bit hard to believe they aren’t more sophisticated than that. However these issues can be dealt with effectively in several ways including - using the noindex meta tag in the non-canonical copies, and 301 server redirects to the canon.

click fraud Improper clicks on a PPC advertisement usually by the publisher or his minions for the purpose of undeserved profit. Click fraud is a huge issue for add agencies like Google, because it lowers advertiser confidence that they will get fair value for their add spend.

cloak The practice of delivering different content to the search engine spider than that seen by the human users. This Black Hat tactic is frowned upon by the search engines and caries a virtual death penalty of the site/domain being banned from the search engine results.

CMS Content Management System - Programs such as Wordpress, which separate most of the mundane Webmaster tasks from content creation so that a publisher can be effective without acquiring or even understanding sophisticated coding skills if they so chose.

code swapping (bait and switch) Changing the content after high rankings are achieved.

comment spam Posting blog comments for the purpose of generating an inlink to another site. The reason many blogs use link condoms.

content (text, copy) The part of a web page that is intended to have value for and be of interest to the user. Advertising, navigation, branding and boilerplate are not usually considered to be content.

contextual advertisement Advertising which is related to the content.

conversion (goal) Achievement of a quantifiable goal on a website. Add clicks, sign ups, and sales are examples of conversions.

conversion rate Percentage of users who convert - see conversion.

CPC Cost Per Click - the rate that is paid per click for a Pay Per Click Advertiser

CPM (Cost Per Thousand impressions) A statistical metric used to quantify the average value / cost of Pay Per Click advertisements. M - from the Roman numeral for one thousand.

crawler (bot, spider) A program which moves through the worldwide web or a website by way of the link structure to gather data.

directory A site devoted to directory pages. The Yahoo directory is an example.

directory page A page of links to related WebPages.

doorway (gateway) A web page that is designed specifically to attract traffic from a search engine. A doorway page which redirects users (but not spiders) to another site or page is implementing cloaking. - Previous Definition revised based upon advice from Michael Martinez

duplicate content Obviously content which is similar or identical to that found on another website or page. A site may not be penalized for serving duplicate content but it will receive little if any Trust from the search engines compared to the content that the SE considers being the original.

e commerce site A website devoted to retail sales.

feed Content which is delivered to the user via special websites or programs such as news aggregators.

FFA (Free For All) A page or site with many outgoing links to unrelated websites, containing little if any unique content. Link farms are only intended for spiders, and have little if any value to human users, and thus are ignored or penalized by the search engines.

frames a web page design where two or more documents appear on the same screen, each within it’s own frame. Frames are bad for SEO because spiders sometimes fail to correctly navigate them. Additionally, most users dislike frames because it is almost like having two tiny monitors neither of which shows a full page of information at one time.

gateway page (doorway page) A web page that is designed to attract traffic from a search engine and then redirect it to another site or page. A doorway page is not exactly the same as cloaking but the effect is the same in that users and search engines are served different content.

gadget see gizmo

gizmo (gadget, widget) small applications used on web pages to provide specific functions such as a hit counter or IP address display. Gizmos can make good link bait.

Google bomb The combined effort of multiple webmasters to change the Google search results usually for humorous effect. The “miserable failure” - George Bush, and “greatest living American” - Steven Colbert Google bombs are famous examples.

Google bowling Maliciously trying to lower a sites rank by sending it links from the “bad neighborhood” - Kind of like yelling “Good luck with that infection!” to your buddy as you get off the school bus - there is some controversy as to if this works or is just an SEO urban myth.

Google dance The change in SERPs caused by an update of the Google database or algorithm. The cause of great angst and consternation for webmasters who slip in the SERPs. Or, the period of time during a Google index update when different data centers have different data.

Google juice (trust, authority, pagerank) trust / authority from Google, which flows through outgoing links to other pages.

Googlebot Google’s spider program

GYM Google - Yahoo - Microsoft, the big three of search

hit Once the standard by which web traffic was often judged, but now a largely meaningless term replaced by pageviews AKA impressions. A hit happens each time that a server sends an object - documents, graphics, include files, etc. Thus one pageview could generate many hits.

hub (expert page) a trusted page with high quality content that links out to related pages.

HTML (Hyper Text Markup Language) directives or “markup” which are used to add formatting and web functionality to plain text for use on the internet. HTML is the mother tongue of the search engines, and should generally be strictly and exclusively adhered to on web pages.

impression (page view) The event where a user views a webpage one time.

in bound link (inlink, incoming link) Inbound links from related pages are the source of trust and pagerank.

index Noun - a database of WebPages and their content used by the search engines.

index Verb - to add a web page to a search engine index.

indexed Pages The pages on a site which have been indexed.

inlink (incoming link, inbound link) Inbound links from related pages are the source of trust and pagerank.

keyword - key phrase The word or phrase that a user enters into a search engine.

keyword cannibalization The excessive reuse of the same keyword on too many web pages within the same site. This practice makes it difficult for the users and the search engines to determine which page is most relevant for the keyword.

keyword density The percentage of words on a web page which are a particular keyword. If this value is unnaturally high the page may be penalized.

keyword research The hard work of determining which keywords are appropriate for targeting.

keyword spam (keyword stuffing) Inappropriately high keyword density.

keyword stuffing (keyword spam) Inappropriately high keyword density.

landing page the page that a user lands on when they click on a link in a SERP

latent semantic indexing (LSI) This mouthful just means that the search engines index commonly associated groups of words in a document. SEOs refer to these same groups of words as “Long Tail Searches”. The majority of searches consist of three or more words strung together. See also “long tail”. The significance is that it might be almost impossible to rank well for “mortgage”, but fairly easy to rank for “second mortgage to finance monster truck team”. Go figure.

link An element on a web page that can be clicked on to cause the browser to jump to another page or another part of the current page.

link bait A webpage with the designed purpose of attracting incoming links, often mostly via social media.

link building actively cultivating incoming links to a site.

link condom Any of several methods used to avoid passing link love to another page, or to avoid possible detrimental results of indorsing a bad site by way of an outgoing link, or to discourage link spam in user generated content.

linkerati internet users who are the most productive targets of linkbait. The Linkerati includes - social taggers, forum posters, resource maintainers, bloggers and other content creators, etc - who are most likely to create incoming links or link generating traffic (in the case of social networkers). Suggested by lorisa.

link exchange a reciprocal linking scheme often facilitated by a site devoted to directory pages. Link exchanges usually allow links to sites of low or no quality, and add no value themselves. Quality directories are usually human edited for quality assurance.

link farm a group of sites which all link to each other.- Previous Definition revised based upon advice from Michael Martinez

link juice (trust, authority, pagerank)

link love An outgoing link, which passes trust, unencumbered by any kind of link condom.

link partner (link exchange, reciprocal linking) Two sites which link to each other. Search engines usually don’t see these as high value links, because of the reciprocal nature.

link popularity a measure of the value of a site based upon the number and quality of sites that link to it

link spam (Comment Spam) Unwanted links such as those posted in user generated content like blog comments.

link text (Anchor text) The user visible text of a link. Search engines use anchor text to indicate the relevancy of the referring site and link to the content on the landing page. Ideally all three will share some keywords in common.

long tail longer more specific search queries that are often less targeted than shorter broad queries. For example a search for “widgets” might be very broad while “red widgets with reverse threads” would be a long tail search. A large percentage of all searches are long tail searches/

LSI(Latent Semantic Indexing) This mouthful just means that the search engines index commonly associated groups of words in a document. SEOs refer to these same groups of words as “Long Tail”. The majority of searches consist of three or more words strung together. See also “long tail”. The significance is that it might be almost impossible to rank well for “mortgage”, but fairly easy to rank for “second mortgage to finance monster truck team”

mashup A web page which consists primarily of single purpose software and other small programs (gizmos and gadgets) or possibly links to such programs. Mashups are quick and easy content to produce and are often popular with users, and can make good link bait. Tool collection pages are sometimes mashups.

META tags Statements within the HEAD section of an HTML page which furnishes information about the page. META information may be in the SERPs but is not visible on the page. It is very important to have unique and accurate META title and description tags, because they may be the information that the search engines rely upon the most to determine what the page is about. Also, they are the first impression that users get about your page within the SERPs.

metric A standard of measurement used by analytics programs.

MFA Made For Advertisements - websites that are designed from the ground up as a venue for advertisements. This is usually, but not always a bad thing. TV programming is usually MFA.

mirror site An identical site at a different address.

monetize To extract income from a site. Adsense ads are an easy way to Monetize a website.

natural search results The search engine results which are not sponsored, or paid for in any way.

nofollow A command found in either the HEAD section of a web page or within individual link code, which instructs robots to not follow either any links on the page or the specific link. A form of link condom.

noindex A command found in either the HEAD section of a web page or within individual link code, which instructs robots to not index the page or the specific link. A form of link condom.

non reciprocal link if site A links to site B, but site B does not link back to site A, then the link is considered non reciprocal. Search engines tend to give more value to non-reciprocal links than to reciprocal ones because they are less likely to be the result of collusion between sites.

organic link organic links are those that are published only because the webmaster considers them to add value for users.

outlink (Out going link)

pagerank (PR) a value between 0 and 1 assigned by the Google algorithm, which quantifies link popularity and trust among other (proprietary) factors. Often confused with Toolbar Pagerank. - Previous Definition revised based upon advice from Michael Martinez

pay for inclusion PFI The practice of charging a fee to include a website in a search engine or directory. While quite common, usually what is technically paid for is more rapid consideration to avoid Googles prohibition on paid links.

portal A web service which offers a wide array of features to entice users to make the portal their “home page” on the web. IGoogle, Yahoo, and MSN are portals.

PPA (Pay Per Action ) Very similar to Pay Per Click except publishers only get paid when click throughs result in conversions.

PPC (Pay Per Click) a contextual advertisement scheme where advertisers pay add agencies (such as Google) whenever a user clicks on their add. Adwords is an example of PPC advertising.

proprietary method (bullshit, snake oil) sales term often used by SEO service providers to imply that they can do something unique to achieve “Top Ten Rankings”.

reciprocal link (link exchange, link partner) Two sites which link to each other. Search engines usually don’t see these as high value links, because of the reciprocal and potentially incestuous nature.

redirect Any of several methods used to change the address of a landing page such as when a site is moved to a new domain, or in the case of a doorway.

regional long tail (RLT) coined by Chris Paston of onlinedevelopment.co.uk - a multi word keyword term which contains a city or region name. Especially useful for the service industry.

RLT see Regional Long Tail

robots.txt a file in the root directory of a website use to restrict and control the behavior of search engine spiders.

ROI (Return On Investment) One use of analytics software is to analyze and quantify return on investment, and thus cost / benefit of different schemes.

sandbox There has been debate and speculation that Google puts all new sites into a “sandbox,” preventing them from ranking well for anything until a set period of time has passed. The existence or exact behavior of the sandbox is not universally accepted among SEOs.

scrape copying content from a site, often facilitated by automated bots. - Definition revised based upon advice from Michael Martinez

SE (Search Engine)

search engine (SE) a program, which searches a document or group of documents for relevant matches of a users keyword phrase and returns a list of the most relevant matches. Internet search engines such as Google and Yahoo search the entire internet for relevant matches.

search engine spam Pages created to cause search engines to deliver inappropriate or less relevant results. Search Engine Optimizers are sometimes unfairly perceived as search engine Spammers. Of course in some cases they actually are.

SEM Short for search engine marketing, SEM is often used to describe acts associated with researching, submitting and positioning a Web site within search engines to achieve maximum exposure of your Web site. SEM includes things such as search engine optimization, paid listings and other search-engine related services and functions that will increase exposure and traffic to your Web site.

SEO Short for search engine optimization, the process of increasing the number of visitors to a Web site by achieving high rank in the search results of a search engine. The higher a Web site ranks in the results of a search, the greater the chance that users will visit the site. It is common practice for Internet users to not click past the first few pages of search results, therefore high rank in SERPs is essential for obtaining traffic for a site. SEO helps to ensure that a site is accessible to a search engine and improves the chances that the site will be indexed and favorably ranked by the search engine.

SERP Search Engine Results Page

site map A page or structured group of pages which link to every user accessible page on a website, and hopefully improves site usability by clarifying the data structure of the site for the users. An XML sitemap is often kept in the root directory of a site just to help search engine spiders to find all of the site pages.

SMWC (Slapping Myself With Celery) indicates an extreme reaction similar to a “spit take” but more vegan-trendy. Often combined with other exclamatory acronyms. - WTF/SMWC, or perhaps ROTFL/SMWC.

SMM (Social Media Marketing) Website or brand promotion through social media

SMP (Social Media Poisoning) A term coined by Rand Fishkin - any of several (possibly illegal) black hat techniques designed to implicate a competitor as a spammer - For example, blog comment spamming in the name / brand of a competitor

sock puppet an online identity used to either hide a persons real identity or to establish multiple user profiles.

social bookmark A form of Social Media where users bookmarks are aggregated for public access.

social media Various online technologies used by people to share information and perspectives. Blogs, wikis, forums, social bookmarking, user reviews and rating sites (digg, reddit) are all examples of Social Media.

social media marketing (SMM) Website or brand promotion through social media

social media poisoning (SMP) A term coined by Rand Fishkin - any of several (possibly illegal) black hat techniques designed to implicate a competitor as a spammer - For example blog comment spamming in the name / brand of a competitor

spam ad page (SpamAd page) A Made For Adsense/Advertisement page which uses scraped or machine generated text for content, and has no real value to users other than the slight value of the adds. Spammers sometimes create sites with hundreds of these pages.

spamdexing Spamdexing or search engine spamming is the practice of deceptively modifying web pages to increase the chance of them being placed close to the beginning of search engine results, or to influence the category to which the page is assigned in a dishonest manner. - Wikipedia

spammer A person who uses spam to pursue a goal.

spider (bot, crawler) A specialized bot used by search engines to find and add web pages to their indexes.

spider trap an endless loop of automatically generated links which can “trap” a spider program. Sometimes intentionally used to prevent automated scraping or e-mail address harvesting.

splash page Often animated, graphics pages without significant textual content. Splash pages are intended to look flashy to humans, but without attention to SEO may look like dead ends to search engine spiders, which can only navigate through text links. Poorly executed splash pages may be bad for SEO and often a pain in the ass for users. - Definition revised based upon advice from Michael Martinez

splog Spam Blog which usually contains little if any value to humans, and is often machine generated or made up of scraped content.

static page A web page without dynamic content or variables such as session IDs in the URL. Static pages are good for SEO work in that they are friendly to search engine spiders.

stickiness Mitigation of bounce rate. Website changes that entice users to stay on the site longer, and view more pages improve the sites “stickiness”.

submission

supplemental index (supplemental results) Pages with very low pagerank, which are still relevant to a search query, often appear in the SERPs with a label of Supplemental Result. Googles representative’s say that this is not indicative of a penalty, only low pagerank. - Previous Definition revised based upon advice from Michael Martinez

text link A plain HTML link that does not involve graphic or special code such as flash or java script.

time on page The amount of time that a user spends on one page before clicking off. An indication of quality and relevance.

toolbar pagerank (PR) a value between 0 and 10 assigned by the Google algorithm, which quantifies page importance and is not the same as pagerank. Toolbar Pagerank is only updated a few times a year, and is not a reliable indicator of current status. Often confused with Pagerank. - Definition added based upon advice from Michael Martinez

trust rank a method of differentiating between valuable pages and spam by quantifying link relationships from trusted human evaluated seed pages.

URL Uniform Resource Locator - AKA Web Address

user generated content (UGC) Social Media, wikis, Folksonomies, and some blogs rely heavily on User Generated Content. One could say that Google is exploiting the entire web as UGC for an advertising venue.

walled garden a group of pages which link to each other, but are not linked to by any other pages. A walled garden can still be indexed if it is included in a sitemap, but it will probably have very low pagerank.

web 2.0 Is characterized by websites, which encourage user interaction.

white hat SEO techniques, which conform to best practice guidelines, and do not attempt to unscrupulously “game” or manipulate SERPs.

widget 1) (gadget, gizmo) small applications used on web pages to provide specific functions such as a hit counter or IP address display. These programs can make good link bait. 2) a term borrowed from economics which means “any product or commodity.”