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.

Algorithmic Results: see Organic Listings.

Backlinks: All the links pointing at a particular web page. Also called inbound links.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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