"In Game Leader", or more casually called the caller is a person on a gaming team, mostly "Counter-Strike" who tells the team what to do, where to go, makes all the decisions.
Originating from the lovely city of Frisco, Texas, "IGL" is an acronym meaning "I get laid" or "I got laid", depending on how it is used. A spin-off of this is "UGL", meaning, of course, "you get laid", used as a question. Used mostly as a joke, such as when a girl asks to borrow a pencil in class and you turn to your friend and excitingly proclaim "IGL!"
Guy #1: Hi, how's it going?
Girl: Good. How about you?
Guy #1: No complaints. Well, bye.
(Girl leaves)
Guy #2: Dude, did UGL?
Guy #1: Right on bro, IGL to the max!