Temperature is a physical quantity that expresses the hotness of matter or radiation.
There are three types of temperature scale: those, such as the SI scale, that are defined in terms of the average translational kinetic energy per freely moving microscopic particle, such as atom, molecule, or electron, in a body; those that rely solely on purely macroscopic properties and thermodynamic principles, such as Kelvin's original definition; and those that are not defined by theoretical principles, but are defined by convenient empirical properties of particular materials.
Three different scales are commonly used to measure temperature: Fahrenheit (expressed as °F), Celsius (°C), and Kelvin (K).