A web site is a location in the internet that contains either lulz or shit nobody cares about. Encyclopedia Dramatica has oodles of information on the most popular web sites. For a list of them, please see the "Sites" category.
There are many different kinds of websites. Some are dedicated almost entirely to forums (i.e. 4chan). Others strive to the collection and organization of info from an unspecified or specified topic. Many news agencies also maintain websites in order to rapidly disseminate lies to their mass of mindless followers.