The term “favicon” refers to a small, square icon usually 16×16 pixels that is associated with a particular website. Web browsers typically display favicons in three places: next to the URL in the address bar, the website’s name in a list of bookmarks, and the page title in browsers that have tabbed browsing.
Favicons are a very tiny detail in a site, but it’s attention to detail that makes a site stand out. From a branding point of view, they’re very important. The main reason for having favicons is to improve user experience.