Thermostat

A thermostat is a sensor which keeps a heating system near to a desired temperature or setpoint. It is a control system.
The thermostat works by switching heating or cooling devices on or off. This is what happens in a central heating system or an air conditioner. In some systems it works by switching a 'heat transfer fluid' off or on as needed to keep the set temperature. The name is derived from the Greek words "thermos" "hot" and "statos" "a standing".
The simplest kind of thermostat is a bimetal strip which bends as the temperature rises, and at a set point breaks the circuit of an electrical current. Kitchen toasters use this kind of thermostat.
Because they control a system, thermostats are examples of feedback devices which maintain a steady local environment against temperature changes outside the outside world. In cybernetics, the thermostat is an example of a machine which uses feedback to maintain the stability of a heating system.