IBM 2790 Manual page 72

PTT: Post Telephone and Telegraph, a generic term for the
government-operated common carrier in each of many
countries.
RTC: Real-Time Clock.
STX: Line-control character, " start of text."
STEND: Mnemonic for a System/360 assembler macro
instruction.
System Controller: The unit, either 2715 or 1800, that
controls the 2790 loop.
TC: Transaction code.
TCU: Transmission Control Unit.
TGROUP: Mnemonic for a System/360 assembler macro
instruction.
Time Stamp: A four-byte field that contains the value of
the Real-Time Clock when the transaction was received.
The time is recorded in 24-hour form as EBCDIC characters.
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TPS: Two-Processor Switch.
Transaction: A sequence of interrelated data entries
entered by the operator at an Area Station or Data Entry
Unit and assembled by the system controller.
Transaction Tables: See "User Transaction Tables."
TRUST: Mnemonic for a System/360 assembler macro
instruction.
UC: Unit Check status bit.
US ASCII: United States of America Standard Code for
Information Interchange.
User Table: See "User Transaction Tables."
User Transaction Tables: Program tables that define the
parameters and controls for the 2790 system. DOS and
OS/360 Assembler Language macros are provided to define
user tables for the 2715.