lsof is a little program that runs on unix derived systems.  It is very powerful.  When I began using linux I learned the most about everything in the unix computing world from it.  WIth it you can see what everything on the system is doing, who owns it, how its connected, and it combines easily and reliably with grep making it an everything tool-think Leathernan instead of Swiss Army knife.  To your average desktop user this is jibberish.  Too bad.  Just know that I am honored to have found it and found my way with it.

http://en.wikipedia.org/wiki/Lsof