, the term transmission block
has the following meanings:
1. A group of bits or characters transmitted as a unit and usually containing an encoding procedure for error control purposes.
2. In data transmission, a group of records sent, processed, or recorded as a unit.
Note: A transmission block is usually terminated by an end-of-block character (EOB), end-of-transmission-block character (ETB), or end-of-text character (EOT or ETX).
Source: from Federal Standard 1037C