JSP query string madness!

I am learning Java Server Pages and I have come across a website that uses JSP and I can’t figure out how they constructued it. They seem to use their index.jsp as some kind of controller for all other pages, for example:

http://www.scient.com/index.jsp?cp=/SC/leadership/main.jsp

It looks like index.jsp is calling the file main.jsp in the directory leadership which is in the directory SC, but I cant figure out what the cp= does and how the whole things works. Can anyone help with this? Ive been struggling for weeks! Thanks!