The measure of the average kinetic energy of particles in a substance is known as temperature. Temperature indicates how hot or cold a substance is and reflects the energy fluctuations of its molecules. Higher temperatures correspond to greater kinetic energy, resulting in increased molecular motion, while lower temperatures indicate slower motion. This concept is fundamental in both physics and chemistry, as it affects states of matter, reaction rates, and energy transfer processes. Temperature measurement is also critical in various scientific applications, from meteorology to engineering.