also: bubble · quick screen
A quick throw to a slot receiver who bubbles backward and outward, with the receivers outside him blocking.
A slot receiver takes a path back and outward, hence bubble, and catches a quick throw almost immediately. The receivers outside him block the defenders over them, and he runs to the space those blocks create.
Its real function is arithmetic rather than deception. If the defense does not put enough defenders over the receivers, the offense has numbers for the throw. If it does, the defense has removed bodies from the box and the run game gets easier. That is why bubble is often attached to a run play rather than called by itself.
bubble, quick screentunnel screen, screen, RPOBubble is very often the pass half of an RPO rather than a called play, which means a coach hearing it may be describing a full play or one branch of another one.