Definition of Alexa on Wikipedia. Discusses Alexa's history, acquisition by Amazon, its partnerships with Google, the Open Directory Project and Windows Live Search, and gives a brief explanation on how Alexa works.

Alexa (owned by Amazon) ranks websites based on information it gathers through the installation of the Alexa toolbar. Information on reach (the number of daily unique visitors) and page views (total user requests for a site) determine a site's ranking, the highest combination of these two factors determine the #1 site. Sites that install the toolbar can see how they rank in relation to any other site.