404 error logs : The server record of every time a page could not be displayed on a Web site.

A/B testing : A comparison between the old version of a Web site (A) and the new version (B) to see which one performs better.

absolute link : A link that contains the whole file path to a document, including the protocol used to get the document (e.g., http://), the server the document is found on (www.mysite.com), the directory it is located in (images), and the document name (vacation.jpg).

acquisition : The measure of users that a Web site attracts. Acquisition metrics come from Web analytics data and include percent of new visitors, average number of visits per visitor, and average pages viewed per visitor.

ad group : One or more ads that target a set of grouped keywords.

advanced search operators : Special terms that you can insert in your search engine query to find specific types of information that a general search can't provide.

algorithm : A mathematical formula a search engine uses to establish which Web pages are the most relevant to a user’s search query. Algorithms can be fairly simple or multi-layered and complex.

anchor text : The words that make up a hyperlink that a user clicks.

archive : A storage area on a server where older Web content is out of the way, but still accessible.

Astro-turfing : A term used for a fake grassroots market campaign; this derives its name from AstroTurf, which is artificial grass.