message part
1. In radio communications, one of the three major subdivisions of a message, namely the heading, the text, or the ending.
Note: Each message part may have separate components and each component may have elements and contents.
2. In cryptosystems, text that results from the division of a long message into several shorter messages of different lengths as a transmission security measure.
Note: Message parts are usually prepared in such a manner as to appear unrelated externally. Statements that identify the parts for assembly at reception are encrypted in the texts. [From Weik ’89]