butt bag noun2 •(US, informal) A fanny pack.The social worker obliged him this, after which Phael abruptly asked for the return of his butt bag and left the room. — 1994 •A seat attached to ropes on which a climber can sit while belaying.Some continuously steep routes with numerous hanging belays necessitate a belay seat or butt bag. A butt bag with three points of suspension is more comfortable than a two-point bag. — 1999 formsbutt bags
