What is a favicon?
A favicon (short for favorite icon), also known as a shortcut icon, website icon, tab icon, URL icon, or bookmark icon, is a very small image, associated with your website or a particular web page.
It will be typically displayed in the browser's address bar, next the page's title on the tab, or next the page's name in a list of bookmarks or in browser history.
The favicon file has .ico extension.
Dimension of a favicon is 16x16 or 32x32
How to create a favicon?
You can make your own favicon using many free on-line tools:
http://favicon.htmlkit.com/favicon/
http://www.favicon.cc/
http://realfavicongenerator.net/