What is a color gamut?

The range of colors that can be formed by all combinations of a given set of light sources or colorants of a color reproduction system.
The normal human eye can perceive a wide gamut of colors, colors within the full range of the visible spectrum, including detail in very bright light and deep shadows.

Transparencies and monitors, which display color using transmitted light, can hold some of that color range, or gamut. Due to such limitations as reflected light, ink impurities, and paper absorption, a conventionally printed image is limited to a much smaller range of colors.