Colour temperature
A way of describing whether white light is yellowish or bluish, given in kelvin.
Also: correlated colour temperature, CCT
Not all white light is the same. Candlelight is orange, a midday sky is bluish. Colour temperature puts a number on this, taken from the colour a glowing hot object would have at that temperature. Low numbers, around 2,700 kelvin, are the yellowish white of old filament bulbs. Around 5,000 to 6,500 kelvin is neutral daylight. Higher still is the blue-white of open shade. Light bulbs are sold by this figure. Confusingly, the lower, yellower numbers are called warm and the higher, bluer ones cool.