A way to see how many people are coming to your site. There are tons of websites/code snippets out there than can do this for you. Some examples are: http://www.sitemeter.com http://www.statcounter.com http://www.digitalpoint.com/tools/counter/ http://www.google.com/analytics/ Do a search in Google for hit counter or website analytics and you're bound to find hundreds more.
It lets you know how many hits you got to your site. Usually you can either pick count every hit or count every different ip address