Payload refers to the object or entity being carried by an aircraft, launch vehicle, or any other transportation medium. Depending on the nature of the flight or mission, the payload of a vehicle may include cargo, passengers, flight crew, munitions, scientific instruments or experiments, or other equipment. Extra fuel, when optionally carried, is also considered part of the payload. In a commercial context, payload may refer only to revenue-generating cargo or paying passengers.

Payload capacity is the amount of weight a vehicle can carry, and towing capacity is the amount of weight it can pull. Payload capacity differs from towing capacity, as the former refers to the weight of everything in the vehicle, including passengers, while the latter refers to the weight a vehicle can pull.

In computing and telecommunications, the payload is the part of transmitted data that is the actual intended message). Headers and metadata are sent only to enable payload delivery and are considered overhead). In the context of a computer virus or worm, the payload is the portion of the malware which performs malicious action).

The term "payload" has its roots in the military and is often associated with the capacity of executable malicious code to do damage. The fraction of payload to the total liftoff weight of the air or spacecraft is known as the "payload fraction". When the weight of the payload and fuel are considered together, it is known as the "useful load fraction". In spacecraft, "mass fraction" is normally used, which is the ratio of payload to everything else, including the rocket structure.