temperature

Temperature is a physical quantity that expresses how hot matter is, or as a measure of the average translational kinetic energy per atom or molecule in the system. It is the detectable portion of the molar thermal energy of matter; a temperature difference allows heat transfer to occur, as energy flows from a hotter body to a colder body.
Temperature is measured with a thermometer. It is calibrated in various temperature scales that historically have relied on various reference points and thermometric substances for definition. The most common scales are the Celsius scale (formerly called "centigrade", with the unit °C), the Fahrenheit scale (with the unit °F), and the Kelvin scale (with the unit K), the latter being used predominantly for scientific purposes and is the primary temperature scale defined by the International System of Units (SI).
The lowest theoretical temperature is absolute zero, at which no more thermal energy can be extracted from a body. Experimentally, it can only be approached very closely, but not reached, which is recognized in the third law of thermodynamics.
Temperature is important in all fields of natural science, including physics, chemistry, Earth science, astronomy, medicine, biology, ecology, material science, metallurgy, mechanical engineering and geography as well as most aspects of daily life.

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