typed body
Technical computing term referring to a body (e.g., in a document or message) that has an associated type identifier, as opposed to an untyped body.
In this protocol, the typed body field indicates the message type.
Compound of 本体 (body, main unit), 種別 (type, classification), and 表示 (display, indication). The exact derivation is uncertain; it is a technical term likely coined in computing contexts.