"Namespace pollution" is where you end up having more symbols in your symbol table than the ones that you put there yourself. It can make things a bit confusing and the chances of having two symbols with the same name is increased. For example, if you have both use CGI ':standard' and use LWP::Simple in your program (which is a pretty common thing to want to do) then both of these modules try to export a subroutine called "head" into your symbol table. This will potentially lead to the universe exploding.