To sit in on a conversation, meeting, card-game or online chat and offer unsolicited, informal comments. The original meaning from Yiddish (kibitzen, derived from German kiebitzen - to be an onlooker or spectator) had a negative connotation of being a busybody or giving intrusive, meddlesome, unwanted advice. However, in contemporary US usage, it has become friendlier.
She's meeting with some suits this afternoon, do you want to come kibitz and liven things up?
I'm not here as a formal participant, I'm just kibitzing.
Like people standing over your shoulder while you are playing chess and they are like talking about your game and making comments and you want to kill them but you turn and say.. "take your kibbitzing elsewherethank you."