A description of the range of visible colors in standardized numerical terms. As human vision is based on three types of light sensor ("red", "green" and "blue" cones) color spaces are usually "3-dimensional".
A color space is a scientifically defined portion of human vision. A color space may be defined with any color model. The RGB values R=10,G=100,B=10 have no meaning by themselves other than the color is greenish. By using a color space definition, the same set of values can be translated into one of the scientific color models, giving the values exact meaning. Having a set of RGB values associated with a color space allows for the exact reproduction of the color.