What is Actio Ad Exhibendum?

Legal Definition
An action for the purpose of compelling a defendant to exhibit a thing or title in his power. It was preparatory to another action, which was always a real action in the sense of the Roman law; that is, for the recovery of a thing, whether it was movable or immovable. Merl. Quest, tome i. 84.
-- Black's Law Dictionary
Legal Definition
A Roman law action to compel the production of goods in the defendants control.
-- Ballentine's Law Dictionary