This is the term that refers to the range of colors that a color space contains.
Colors are described as being "out of gamut" when there is no representation of the color in the space in question. For example, a full sRGB "white" is out of gamut for printing where an absolute "rendering intent" is requested, for the simple reason that the paper would have to glow to reproduce it correctly.
Most common color spaces do not have a gamut that fully encompass that of human vision, and so when converting between color spaces some compromise is necessary since not all colors can be mapped into the new space. The rendering intent controls this compromise.