defined checks whether or not a key is defined in a hash, in this context it will return true if the name was found in your file 1. lc turns a string into lower case, adding a bit of robustness to the code (I assumed you wanted to do case insensitive matching).

Generally, there is excellent documentation at http://perldoc.perl.org should you be unfamiliar with a specific function.

UPDATE: It seems I was a bit tired when writing in this thread. While defined does the job, one really should be using exists. Apologies! A simple introduction into hashes can be found here http://www.tutorialspoint.com/perl/perl_hashes.htm but googling "perl hash" will lead to many more good hits.