1. The load carried by a vehicle exclusive of what is necessary for its operation; especially; the load carried by an aircraft or spacecraft consisting of things (as passengers or instruments) necessary to the purpose of the flight
2. The weight of a payload

The effects caused by a virus or other malicious code. The payload of a virus may include moving, altering, overwriting, and deleting files, or other destructive activity. A virus or worm may contain more than one payload, each with a separate trigger.