This four ink color printing system (using Cyan, Magenta, Yellow and blacK inks) is very commonly used to represent image data that has been prepared for printing (even if the component values are not exactly what the printer will be using). There are also two commonly used standardized CMYK systems which allow CMYK data to be used in a printer-independent manner, called "Euroscale" and "SWOP".
Although there is a simplistic way to convert between CMYK and RGB data, this doesn't usually result in colors being correctly represented. A major factor is that RGB color spaces are designed for luminous devices, whereas CMYK systems are designed for making colors on (usually white) paper. So while RGB devices are capable of generating quite bright light, for CMYK systems the maximum light that can be generated can never exceed, and is dependent on, the light that illuminates the paper. Even white paper doesn't reflect all the incident light so this creates a substantial mismatch between RGB and CMYK systems.