Favicon - How To Create A Favicon.ico | PhotoshopSupport.com
www.photoshopsupport.com/tutorials/jennifer/favicon.html
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
A Favicon is a little custom icon that appears next to a website's URL in the address bar of a web browser. And when I say little, I mean 16 pixels by 16 pixels. So if you like a good design challenge try your hand at this one.