A picture bid is a bid which nearly describes the hand completely.
Example[]
A disciplined preemptive opening is a picture bid, because it perfectly describe the strength and shape of the opener. For example, if a 2♥ opening is disciplined, it is expected that the shape will be likely 6-3-2-2, with the majority of high cards in ♥s. Afterwards, the responder can directly bid to the expected contract simply according the opening.