Colour temperature is a scale that measures how warm (yellow) or cool (blue) the light from a particular source is. It is measured in degrees of the kelvin scale (K) and the higher the number the cooler the light. The lower the number the warmer the light.

2700 – 3000K Warm White

Lamps in this range are normally found in a domestic setting

4000K Cool White

Lamps in this range are normally found in a commercial setting giving good colour, a clean light which is also often used to illuminate new bathrooms and kitchens

5000 - 6500K Daylight White

Lamps in this range can boost alertness and productivity ideal for home offices and classrooms

Some lamps or luminaires are now colour selectable and can be switched between warm/cool/daylight 

Personally speaking, I prefer cool white myself for kitchens, bathrooms, office, etc however I do find warm white a better choice for the living room when chilling in front of the tele