A remote terminal unit (RTU) is a microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

-controlled electronic device that interfaces objects in the physical world to a distributed control system

Distributed control system

A distributed control system refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location but are distributed throughout the system with each component sub-system controlled by one or more...

 or SCADA

SCADA

SCADA generally refers to industrial control systems : computer systems that monitor and control industrial, infrastructure, or facility-based processes, as described below:...

 (supervisory control and data acquisition system) by transmitting telemetry

Telemetry

Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...

 data to the system and/or altering the state of connected objects based on control messages received from the system. Another term that may be used for RTU is remote telemetry unit, the common usage term varies with the application area generally.
An RTU monitors the field digital and analog parameters and transmits all the data to the Central Monitoring Station.