The Favicon is an tiny icon that is used by webmaster to put the brand of the website they maintain in the tabs and lists of websites that the end users have in their browsers.
The favicon plugin is just administrative settings that let you drag and drop a .ico file to use as your favority icon. The system also offers some default favicon that you can freely use.
At this time we accept ICO, PNG, and JPEG images. The ICO may include multiple sizes, which is a good idea for Macintosh users since OS/X tends to make use of larger icons (up to 192x192).