When a physicist speaks of temperature, he means the measure of energy inherent in a body. This energy is possessed by a body due to the random motion of its atoms or molecules. If the particles move faster, then the temperature increases. Temperature is thus a state variable. Together with mass, heat capacity and others, temperature describes the energy content of a body, or, as it often expressed in physics, a system.
Or more briefly:
- Introduction of heat energy leads to an increase of particle speed: Temperature increases
- Introduction of heat energy leads to a decrease of particle speed: Temperature decreases