Shortcut icon
The shortcut icon, or favicon, is the icon shown by the browser next to a website's address. The browser always tries to use a favicon, even if you didn't specify one. As a result, if that icon is not in browser cache, the browser will request it each time it opens a page on your site. This means that even if you don't care about the shortcut icon itself, it still makes sense to provide one simply to stop the browser from requesting it over and over again.
The shortcut icon is a little image in ICO format. There are many programs and websites that let you convert a png image to ICO format such as http://www.convertico.com.
One way to give the icon to the browser is to name it favicon.ico and put it in the root folder of your site. However, if you decide to change the icon, then all the visitors whose browsers still have favicon.ico in their browser cache will continue to see the old icon.
A better way is to explicitly link to the shortcut icon in the head of each web page. That...
