A ball transfer unit (BTU) is a device used to facilitate the movement of heavy or awkwardly shaped objects. It consists of a series of small balls mounted on a plate, which can rotate in any direction. The object to be moved is placed on top of the balls, and then the unit can be rolled in any direction, allowing the object to be moved easily and quickly without having to lift it. BTUs are often used in factories or warehouses to move heavy objects around, or in office settings to move furniture or equipment.