Favicon terminology

Following the lead of the Wikipedia article on favicons, I define the term favicon to mean an icon displayed by a browser anywhere outside its viewport to signify a website or webpage. A browser’s viewport is the area of a browser window where the current page is rendered.

Favicon is a taxonomic term that sweeps together different kinds of images manipulated in different ways by different products. More specific terms are useful to distinguish different classes of favicon that may be characterized by mutually-exclusive properties. I have absconded with words from the Wikipedia definition to form the terms described in this table of Favicon Terms. A favicon link is an HTML link tag with with a rel attribute value of either "icon" or "shortcut icon".

favicon term	invoked by	applies to	source	image type see note	persistence	display context
webpage favicon	favicon link	specific page in a web domain	any URL	ICO GIF JPG PNG TIFF	cached	current page
website favicon	absence of favicon link	any page in a web domain without a webpage favicon	favicon.ico in a web domain's root folder	ICO	cached	current page
bookmark favicon	saving a webpage favicon or a website favicon	any page in a web domain	any URL	ICO GIF JPG PNG TIFF	saved	hyperlink

Note: The MIME type for a website favicon must be image/vnd.microsoft.icon or image/x-icon. The MIME type for a webpage favicon (a) may designate any image format native to a browser and (b) should be a well-formed IANA media type name, preferably a registered name.

Note: There may be other constraints on bookmark favicons, such as a limit on the physical size of the image file.

Note: I received 13,300,000 Google hits for favicon, 2,550,000 for page icon, 838,000 for site icon, 520,000 for bookmark icon, 95,500 for favorites icon, and 18,700 for domain icon. By this measure, favicon is the most widely used of these terms. In contrast, Google reported only 20 hits for webpage favicon, 617 for website favicon, and 438 for bookmark favicon, so I feel comfortable expropriating these terms.