Short name for "Favorites Icon". It's an icon associated with a particular website or webpage. In most browsers favicon appears next to the web address of browser's URL bar at the top of the page, also favicons are displayed in lists of bookmarks and tabbed document interface.
In early browsers, identical icons where used for all websites on the web. For example: Netscape Navigator used icon in the shape of folder, in Microsoft Internet Explorer small letter «e». Nowadays most of the browsers designed to use icon of the website you visit.