The average amount of time it takes to kill an opponent in a firefight.
Games with higher TTK are generally harder and require more skill as it gives the target the opportunity to return fire and/or take cover.
"Why haven't you joined ToonTask yet? It'll be easier for us to communicate."
The term TTK in regards to smoking a blunt and holding a beer during doggy style intercourse and ejaculating on the girls back, shouting "TTK!!!" was coined by the same two students.