ALGORITHM:
A set of rules that a search engine uses to rank the listings contained within its index, in response to a particular query. No search engine reveals exactly how its own algorithm works, to protect itself from competitors and those who wish to spam the search engine. Source: Did-It.com

BACKLINKS:
All the links pointing at a particular web page. Also called inbound links. Source: Webmaster World Forums

BANNED:
When pages are removed from a search engine's index specifically because the search engine has deemed them to be spamming or violating some type of guidelines.

CLICKTHROUGH RATE:
The percentage of those clicking on a link out of the total number who see the link. For example, imagine 10 people do a web search. In response, they see links to a variety of web pages. Three of the 10 people all choose one particular link. That link then has a 30 percent clickthrough rate. Also called CTR. Source: Webmaster World Forums

CLOAKING:
In terms of search engine marketing, this is the act of getting a search engine to record content for a URL that is different than what a searcher will ultimately see. It can be done in many technical ways. Several search engines have explicit rules against unapproved cloaking. Those violating these guidelines might find their pages penalized or banned from a search engine's index. As for approved cloaking, this generally only happens with search engines offering paid inclusion program. Anyone offering cloaking services should be able to demonstrate explicit approval from a search engine about what they intend to do. If not, then they should then have explained the risks inherent of unapproved cloaking.

CONTEXTUAL LINK INVENTORY
To supplement their business models, certain text-link advertising networks have expanded their network distribution to include "contextual inventory". Most vendors of "search engine traffic" have expanded the definition of Search Engine Marketing to include this contextual inventory. Contextual or content inventory is generated when listings are displayed on pages of Web sites (usually not search engines), where the written content on the page indicates to the ad-server that the page is a good match to specific keywords and phrases. Often this matching method is validated by measuring the number of times a viewer clicks on the displayed ad.

CONVERSION RATE:
The relationship between visitors to a web site and actions consider to be a "conversion," such as a sale or request to receive more information. Often expressed as a percentage. If a web site has 50 visitors and 10 of them convert, then the site has a 20 percent conversion rate. Source: Webmaster World Forums

COST PER CLICK:
System where an advertiser pays an agreed amount for each click someone makes on a link leading to their web site. Also known as CPC. Source: Webmaster World Forums

CPC:
see Cost Per Click.

CPM:
System where an advertiser pays an agreed amount for the number of times their ad is seen by a consumer, regardless of the consumer's subsequent action. Heavily used in print, broadcasting and direct marketing, as well as with online banner ad sales. CPM stands for "cost per thousand," since ad views are often sold in blocks of 1,000. The M in CPM is Latin for thousand. Source: Webmaster World Forums and Did-It.com

CRAWLER:
Component of search engine that gather listings by automatically "crawling" the web. A search engine's crawler (also called a spider or robot), follows links to web pages. It makes copies of the web pages found and stores these in the search engine's index.

CTR:
see Clickthrough Rate.

DELISTING:
When pages are removed from a search engines index. This may happen because they have been banned or for other reasons, such as an accidental glitch on the search engine's part. Source: Adventive

DIRECTORIES:
A type of search engine where listings are gathered through human efforts, rather than by automated crawling of the web. In directories, web sites are often reviewed, summarized in about 25 words and placed in a particular category.

DOORWAY PAGE:
A web page created expressly in hopes of ranking well for a term in a search engine's non-paid listings and which itself does not deliver much information to those viewing it. Instead, visitors will often see only some enticement on the doorway page leading them to other pages (i.e., "Click Here To Enter), or they may be automatically propelled quickly past the doorway page. With cloaking, they may never see the doorway page at all. Several search engines have guidelines against doorway pages, though they are more commonly allowed in through paid inclusion programs. Also referred to as bridge pages, gateway pages and jump pages, among other names.

GATEWAY PAGE:
see Doorway Page.

GRAPHICAL SEARCH INVENTORY
. Banners, and other types of advertising units which can be synchronized to search keywords. Includes pop-ups, browser toolbars and rich media.

INDEX:
The collection of information a search engine has that searchers can query against. With crawler-based search engines, the index is typically copies of all the web pages they have found from crawling the web. With human-powered directories, the index contains the summaries of all web sites that have been categorized.

INBOUND LINK:
See Backlinks.

KEYWORDS:
See Search Terms.

LANDING PAGE:
The specific web page that a visitor ultimately reaches after clicking a search engine listing. Marketers attempt to improve conversion rates by testing various landing page creative, which encompasses the entire user experience including navigation, layout and copy. Source: Did-It.com

LINK POPULARITY:
A raw count of how "popular" a page is based on the number of backlinks it has. It does not factor in link context or link quality, which are also important elements in how search engines make use of links to impact rankings.

LINK TEXT:
The text that is contained within a link. For example, search engine is a link that contains the link text "search engine."

LISTINGS:
The information that appears on a search engine's results page in response to a search.

META SEARCH ENGINE:
A search engine that gets listings from two or more other search engines, rather than through its own efforts.

META TAGS:
Information placed in a web page not intended for users to see but instead which typically passes information to search engine crawlers, browser software and some other applications.

META DESCRIPTION TAG:
Allows page authors to say how they would like their pages described when listed by search engines. Not all search engines use the tag.

META KEYWORDS TAG:
Allows page authors to add text to a page to help with the search engine ranking process. Not all search engines use the tag.

META ROBOTS TAG:
Allows page authors to keep their web pages from being indexed by search engines, especially helpful for those who cannot create robots.txt files. The Robots Exclusion page provides official details.

ORGANIC LISTINGS:
Listings that search engines do not sell (unlike paid listings). Instead, sites appear solely because a search engine has deemed it editorially important for them to be included, regardless of payment. Paid inclusion content is also often considered "organic" even though it is paid for. This is because that content usually appears intermixed with unpaid organic results.

OUTBOUND LINKS:
Links on a particular web page leading to other web pages, whether they are within the same web site or other web sites.

PAID INCLUSION:
Advertising program where pages are guaranteed to be included in a search engine's index in exchange for payment, though no guarantee of ranking well is typically given. For example, Looksmart is a directory that lists pages and sites, not based on position but based on relevance. Marketers pay to be included in the directory, on a CPC basis or per-URL fee basis, with no guarantee of specific placement. Also see XML Feeds. Source: Did-It.com

PPC:
Stands for pay-per-click and means the same as cost-per-click. See Cost Per Click.

PAID LISTINGS:
Listings that search engines sell to advertisers, usually through paid placement or paid inclusion programs. In contrast, organic listings are not sold.

PAY-FOR-PERFORMANCE:
Term popularized by some search engines as a synonym for pay-per-click, stressing to advertisers that they are only paying for ads that "perform" in terms of delivering traffic, as opposed to CPM-based ads, where ads cost money, even if they don't generate a click.

PAY-PER-CLICK:
see Cost Per Click.

PAID PLACEMENT:
Advertising program where listings are guaranteed to appear in response to particular search terms, with higher ranking typically obtained by paying more than other advertisers. Paid placement listings can be purchased from a portal or a search network. Search networks are often set up in an auction environment where keywords and phrases are associated with a cost-per-click (CPC) fee. Overture and Google are the largest networks, but MSN and other portals sometimes sell paid placement listings directly as well. Portal sponsorships are also a type of paid placement.

POSITION:
See Rank.

QUERY:
See Search Terms.

RANK:
How well a particular web page or web site is listed in a search engine results. For example, a web page about apples may be listed in response to a query for "apples." However, "rank" indicates where exactly it was listed -- be it on the first page of results, the second page or perhaps the 200th page. Alternatively, it might also be said to be ranked first among all results, or 12th, or 111th. Overall, saying a page is "listed" only means that it can be found within a search engine in response to a query, not that it necessarily ranks well for that query. Also called position.

RECIPROCAL LINK:
A link exchange between two sites. Source: Webmaster World Forums

REGISTRATION:
See Submission.

RESULTS PAGE:
After a user enters a search query, the page that is displayed, is call the results page. Sometimes it may be called SERPs, for "search engine results page." Source: Webmaster World Forums

ROBOT:
see Crawler.

ROBOTS.TXT:
A file used to keep web pages from being indexed by search engines. The Robots Exclusion page provides official details.

ROI:
Stands for "Return On Investment" and refers to the percentage of profit or revenue generated from a specific activity. For example, one might measure the ROI of a paid listing campaign by adding up the total amount spent on the campaign (say $200) versus the amount generated from it in revenue (say $1,000). The ROI would then be 500 percent. Source: Did-It.com

SEARCH ENGINE:
Any service generally designed to allow users to search the web or a specialized database of information. Web search engines generally have paid listings and organic listings. Organic listings typically come from crawling the web, though often human-powered directory listings are also optionally offered. Source: Webmaster World Forums

SEARCH ENGINE MARKETING:
The act of marketing a web site via search engines, whether this be improving rank in organic listings, purchasing paid listings or a combination of these and other search engine-related activities.

SEARCH ENGINE OPTIMIZATION:
The act of altering a web site so that it does well in the organic, crawler-based listings of search engines. In the past, has also been used as a term for any type of search engine marketing activity, though now the term search engine marketing itself has taken over for this. Also called SEO.

SEARCH TERMS:
The words (or word) a searcher enters into a search engine's search box. Also used to refer to the terms a search engine marketer hopes a particular page will be found for. Also called keywords, query terms or query.

SEM:
Acroymn for search engine marketing and may also be used to refer to a person or company that does search engine marketing (i.e.., "They're an SEM firm).

SEMPO:
Search Engine Marketing Professional Organization, a non-profit, formed to increase the awareness of and educate people on the value of search engine marketing.

SEO:
Acronym for search engine optimization and often also used to refer to a person or company that does search engine optimization (i.e., "They do SEO").

SERPS:
see Results Page.

SHOPPING SEARCH:
Shopping search engines allow shoppers to look for products and prices in a search environment. Premium placement can be purchased on some shopping search indices.

SPAM:
Any search engine marketing method that a search engine deems to be detrimental to its efforts to deliver relevant, quality search results. Some search engines have written guidelines about what they consider to be spamming, but ultimately any activity a particular search engine deems harmful may be considered spam, whether or not there are published guidelines against it. Example of spam include the creation of nonsensical doorway pages designed to please search engine algorithms rather than human visitors or heavy repetition of search terms on a page (i.e. the search terms are used tens or hundreds or times in a row). These are only two of many examples. Determining what is spam is complicated by the fact that different search engines have different standards. A particular search engine may even have different standards of what's allowed, depending on whether content is gathered through organic methods versus paid inclusion. Also referred to as spamdexing. Source: Webmaster World Forums

SPIDER:
See Crawler.

SUBMISSION:
The act to submitting a URL for inclusion into a search engine's index. Unless done through paid inclusion, submission generally does not guarantee listing. In addition, submission does not help with rank improvement on crawler-based search engines unless search engine optimization efforts have been taken. Submission can be done manually (i.e., you fill out an online form and submit) or automated, where a software program or online service may process the forms behind the scenes.

QUERY:
See Search Terms.

XML FEEDS:
A form of paid inclusion where a search engine is "fed" information about pages via XML, rather than gathering that information through crawling actual pages. Marketers can pay to have their pages included in a spider based search index either annually per URL or on a CPC basis based on an XML document representing each page on the client site. New media types are being introduced into paid inclusion, including graphics, video, audio, and rich media.