The CIE and CCT are in effect shorthand labels for the human visual response to observed colour. The CIE system (or CIE Standard Observer Tristimulus colorimetry) is a remarkably successful tool that is used worldwide. Its first key feature is that it relates the spectral power distribution (or SPD) of light stimuli to the visual sensation it causes. The next feature is that it enables all visual colour sensations thus created to be labelled with a well-defined colour identity (called its CIE XYZ Tristimulus co-ordinates). Finally, it also accurately predicts the visual result of colour mixture, for example when making up dye recipes. The CCT successfully characterises the apparent colour of daylight (and alternate light sources) by relating it physically to the light emitted by very hot objects, think if you will of the sun, fires and welding. The point is, the SPD of such light sources follows the precise well defined law of black body radiation.

The International Commission on Illumination (CIE) is non-profit research organization. You can find more information here http://www.cie.co.at/about-cie

As David already mentioned, correlated color temperature (CCT) is used to define the color appearance of light sources. It is an imperfect, but widely used, quantity to describe and communicate color information for light sources.

If you are interested in lighting, it is good to be familiar with these terms, regardless of what you want to do (e.g. design, research).

color space CIE1976 Lab is suitable for the representation and calculation of all object colors. It is widely adopted by all countries in the world, and taken as an international color measuring system. in gemological research, CIE colorimetry theory is applied in quantitative description of gemstone color.