Backdrive refers to the ability of a mechanical system or device to be manually manipulated or moved by an external force, typically in the opposite direction of its normal operation. In other words, it refers to the ability to manually override or move a system that is primarily powered or controlled by another source. In many mechanical systems, such as gears, motors, or actuators, backdrive can occur when an external force is applied to the system, causing it to move or rotate in a direction opposite to its intended operation. This can happen when the system's power source is disengaged or when there is a mechanical or external force acting on the system.