Perl is short for 'Practical Extraction and Report Language', and is both a simple and powerful language to use. Perl is a scripting language, which means that programs do not have to be compiled, before they are executed. Scripts are just a bunch of statements thrown into a file and a Perl program is just that. It is easy to use because it borrows from existing languages like awk and c, but comes with many more features which are not available in those languages. Perl is most renowned for its regular expressions, modules, eval statements, etc. In short is is very useful for creating very powerful algorithms with (almost) as little effort as possible.
Since there are many Perl tutorials on the net, I will not go into the Perl syntax here, but provide you with some useful links. Max Planck intranet users should really check the Perl online books available at our institute!