Measured in Kelvin. The colour temperature describes the perceived colour impression of a light source.
For example, a lamp with 3000K is perceived as warm light and one with 6000K as cold light.
Our D50 standard light has a colour temperature of 5000K.
Kelvin is an absolute temperature unit, which is used in science.
The color temperature is in Kelvin of a light source, a monitor or an image corresponds to the temperature of a perfectly black object, that would glow at this temperature.
Daylight is defined with 6500 Kelvin, standardized light for commercial printers and prepress in Europe is considered as D50 standard light with a color temperature of 5000 Kelvin.
The word “degrees” is incidentally not used in conjunction with Kelvin. A temperature of 5000 Kelvin is not referred to as “5000 degrees Kelvin,” but only over 5000 Kelvin or “K 5000”.