As it applies to graphic art, gamut refers to the complete range of color available. Variables include inks, paper and lighting. Different color spaces offer overlapping but not identical gamuts.
The gamut of RGB colors is affected by the model used to define colors. There are actually different RGB spaces. The most common used by computer displays, digital cameras, and the default for Adobe Creative Suite is sRGB because it reproduces brighter colors and approximates the color gamut of various computer displays. For this reason, it used for images displayed on the Internet. However, Adobe RGB (1998) improves upon the later gamut (~25% shadow, ~50% midtone, and ~75% highlight) primarily in cyan-greens so it is more commonly used by graphic designers for print.
As evidenced from gamut comparison, converting an Adobe RGB (1998) image to sRGB truncates its range of color. However, if sRGB is converted to Adobe RGB (1998) colors range is not dynamically expanded.
Wide Gamut RGB and ProPhoto RGB significantly extend color range beyond Adobe RGB (1998). However, their extremes can result in severe color shifts if output device or paper selection do not support the range.