A metric unit of temperature.
Definition: One degree is 1/273.16 of the difference between the triple point of water (at exactly 0.01°C) and absolute zero.
The triple point of water is the temperature at which water can exist simultaneously in the gaseous, liquid, and solid states. Absolute zero is the temperature at which all molecular motion discontinues.
The Celsius temperature scale is named for the Swedish astronomer and physicist Anders Celsius (1701-1744), who used a similar scale.

See also Kelvin, Fahrenheit.

(K) The SI unit of temperature.
Definition: One Kelvin is 1/273.16 of the difference between the triple point of water (at exactly 273.16 K) and absolute zero.
The triple point of water is the temperature at which water can exist simultaneously in the gaseous, liquid, and solid states. Absolute zero is the temperature at which all molecular motion discontinues. 0 K is according to -273.15° Celsius and -459° Fahrenheit.