A series of words that a user types into a search engine to find a resource. Website owners often perform elaborate keyword analyses to predict what term the searcher may use in a search engine in hope of finding their website. Site owners will optimize their sites in order to gain visibility in the search engines in hope of generating traffic to their site when users type various key phrases into search engines.

Depending on how far a user may be in their information gathering, research or buying cycle, the number of key phrases they use may vary. An initial search may consist of a single keyword or a two word phrase. A more advanced (specific) search may consist of a search for a 4 or 5 word key phrase.