A power take-off or power takeoff (PTO)

is any of several methods for taking power from a power source, such as a running engine,

and transmitting it to an application such as an attached implement or separate machines.

Most commonly,

it is a splined drive shaft installed on a tractor or truck allowing implements with mating fittings to be powered directly by the engine.

Semi-permanently mounted power take-offs can also be found on industrial and marine engines.

These applications typically use a drive shaft and bolted joint to transmit power to a secondary implement or accessory.

In the case of a marine application, such shafts may be used to power fire pumps.

In aircraft applications, such an accessory drive may be used in conjunction with a constant speed drive.

Jet aircraft have four types of PTO units: internal gearbox, external gearbox,

radial drive shaft, and bleed air, which are used to power engine accessories.

In some cases, aircraft power take-off systems also provide for putting power into the engine during engine start..