If you’ve ever printed anything with a commercial print service, it’s likely you’ve heard the term CMYK. The acronym stands for Cyan (blue-green), Magenta (deep purplish red), Yellow, and Key: those are the colors used in printing presses to make up images from four specific color plates of ink dots. It's called 'Key' because black is actually considered one of the main colours; we call them all by their acronyms so that they're easier to remember when designing prints or laying out files properly before sending off projects!
Most printers use CMYK because it's easier to standardize than RGB. Not only is the color spectrum for this type of printer more uniform, but there are so many minute variations in colors that they can't afford not to be consistent with every print run and between different runs.
Most commercial printers will just print in CMYK instead of both types (RGB) because printing in this format makes consistency much simpler throughout a whole production process or even multiple productions which most companies cannot risk when dealing with products like prints where small details matter greatly.