Temperature:

The hotness or coldness of a piece of plastic, metal, wood, or other material depends upon the molecular activity of the material.  Kinetic energy is a measure of the activity of the atoms that make up the molecules of some material. Thus, temperature is a measure of the kinetic energy of the material within question.

Whether you need to know the temperature of the surrounding air and the water cooling a car's engine, or the elements of a nuclear facility, you must have a few means to measure the kinetic energy of the material. Many temperature measuring devices use the energy of the material or system they are monitoring to increase (or lower) the kinetic energy of the device. The general household thermometer is one example.  Mercury, or other liquid, within the bulb of the thermometer expands as its kinetic energy is raised.  Through observing how far the liquid rises within the tube, you could tell the temperature of the measured object.

Since temperature is one of the most important parameters of a material, several instruments have been established to measure it. One category of detector used is the resistance temperature detector (RTD).  The RTD is used at several DOE nuclear facilities to measure temperatures of the procedure or materials being monitored.