An Internet service offered by Microsoft for their Xbox video game system, for the sake of being able to play their Xbox games online. Comes with a microphone so that you can speak to the other people you are playing with.
Sadly, most Xbox owners are not used to being able to talk to their opponents like PC gamers are. Hence the majority of the conversation that goes on often consists of "YOU MOTHER FUCKER!!! SHOOT THE FUCKING GUY!!!"