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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 is borrowed from transportation, where payload refers to the part of the load that pays for transportation. ...
The term "payload" in computing terms can mean several different things.
1) In computer networking, a payload is the part of a data packet containing the transmitted data.
2) In computer security, a payload is the part of a computer virus or other malware containing the code that carries out the virus's harmful activity.
1. Data Packet Payload
A payload is the part of a protocol data unit (PDU) that contains the transmitted data or message. When one device sends data over a network, it needs to combine that data with a header into a packet. A packet's header contains directions from its origin to its destination and instructions on how to reassemble the payload. Once the destination device receives the packet, it discards the header and then reads the data in the payload—much like receiving and opening a letter, discarding the envelope, then reading the message. ...