This is the recognized system of classifying the visual perception of how colour appears to the eye, it's abbreviated as "CCT".
Colour temperature is determined by the ratios of the individual colours which together make up its total spectral distribution. The combination of these results in a single figure categorizes not only the individual lamp but also all production of that particular named group i.e. "Warm White, Daylight, Cool White" etc.
This system relies on a "Kelvin" classification.
This is commonly expressed as 2700K – Warm White / 4000K – Daylight or Natural White / 6500K – Cool White