The lag between replies in an IM-style conversation: one person types a new statement BEFORE the other person types his/her reply to a previous statement, thus making it unclear in a humorous, surprising or even tragic way.
Eli: I just got accepted to go on the space shuttle.
Nina: Oh wow!
Eli: Oh, and one other thing.
Nina: You must be so excited!
Eli: I think my condom broke last night.
Nina: That's SO AMAZING!
Eli: Uh, chatgap?
Nina: Oh, snap! Chatgap!