Temperature is defined as the energy level of matter which can be evidenced by some change in that matter.

Temperature is a very critical and widely measured variable for most mechanical engineers. Many processes must have either a monitored or controlled temperature. This can range from the simple monitoring of the water temperature of an engine or load device, or as complex as the temperature of a weld in a laser welding application. Much more common are the temperatures of fluids in processes or process support applications, or the temperature of solid objects such as metal plates, bearings and shafts in a piece of machinery.

The basic types of temperature measuring sensors are thermocouples, resistive temperature devices (RTDs), infrared radiators, bimetallic devices.