correlated color temperature
Correlated color temperature (CCT) describes the relative color appearance of a white light source, indicating whether it appears more yellow/gold or more blue, in terms of the range of available shades of white.
CCT is given in kelvin (the SI unit of absolute temperature) and refers to the appearance of a theoretical blackbody heated to high temperatures. As the blackbody gets hotter, it turns red, orange, yellow, white, and finally blue. The CCT of a light source is the temperature (in K) at which the heated blackbody matches the color of the light source in question.