Backdriving is when a component is used in reverse to obtain its input from its output. This extends to many concepts and systems from thought based to practical mechanical applications.

Not every system can be backdriven. A DC electrical generator

Electrical generator

In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...

 can be implemented by backdriving a DC electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

, however a worm drive

Worm drive

A worm drive is a gear arrangement in which a worm meshes with a worm gear...

works only in one direction.

Example: A CNC vertical mill has a vertical lead screw on the Z-axis. A low lead screw pitch (i.e. 5 turns per inch or fewer) means when the driving motor power is removed such as by turning the machine off, the weight of the spindle will cause the lead screw to rotate as the spindle motor falls down. Obviously this is a bad thing. The solution to prevent back-driving is to use a finer (higher) lead screw pitch (i.e. 10tpi or greater) or have a locking mechanism.