about the site , Addtion in the sence it could be logo,company Profile, company production,web site application, and so many .
here are the top most Example of the fevicon sites
now how u can do this
its very simple to do , just u need to add some line's of code and be ready with small icon image, u can also add animated image in fevicon
add this part in between <head> </head> Section
<link rel="shortcut icon" href="images/favicon.ico">
now some time this code will not work on most of the Browser like IE old version
in this case u can add this line
<link rel="shortcut icon" href="images/favicon.ico" type="image/vnd.microsoft.icon" *gt;
any other query plz comment on it.