Slayer. Deathmatch. Arena. Free-for-all. The mode has many names, but your aim stays the same: kill everyone, as many times as possible. Maybe there's a time limit or a kill limit, but it usually comes down to some variation of "the person or team with the most kills wins." Simple, seductive...and kind of mindless.
There were so much discussion and so many questions spurred by the two videos I posted from Gears of War 3 this morning that I went back to Microsoft for a walk-through of everything we were seeing in clips.