Remote transmission (terminal) unit used in telemetry (SCADA) systems to transmit operating information to a master terminal unit (MTU) usually located in a control center.
Source: IADC UBO / MPD Glossary, December 2011. Global Standards
Remote Terminal Unit.
Source: ANSI/ISA–99.00.01–2007, Security for Industrial Automation and Control Systems, Part 1: Terminology, Concepts, and Models, 29 October 2007. National Standard