Payload
A payload is the data carried by a request or response, distinct from its envelope: headers, routing information, and metadata. In an HTTP context, the payload is the body of the message: a JSON object, an XML document, form data, or a binary stream.
The term is also used outside HTTP: a queue message has a payload, a JWT has a payload, and a webhook notification carries a payload describing the event.
The request payload is typically read from php://input for raw bodies, or accessed through framework helpers that parse and validate it.
<?php
$payload = json_decode(file_get_contents('php://input'), true);
?>