The whole topic of color management can get pretty dry and technical, but stick with it because there’s information here that’s useful and puts lots of other things in context.
CMYK
This is a color model used in printing processes, where colors are defined in terms of cyan, magenta, yellow and black color channels (black is represented by the letter ‘K’). Desktop printers use CMYK inks but carry out the conversion from regular RGB photos automatically. In commercial printing, a designer will convert a regular RGB photo to CMYK to check the color rendition and prepare it for printing.