RGB and CMYK are colour models that (in simple terms) define what colours are available for you to work with. Within these colour models, there are different colour profiles that meet specific requirements.

About CMYK

CMYK has always been associated with print and is based on the process of using Cyan, Magenta, Yellow and Key (Black) to print images and documents.

Production printers (Brochures/Business Cards) and instant photo printing labs use CMYK as the cost of creating prints with less colours is faster and much more cost effective.

It also significantly reduces the colour range of your prints.

About RGB

RGB is based on how screens display colours using Red, Green and Blue + White. It has become the default colour model for fine art printing as it accommodates a much larger range of colours.

We use 12 different colours in our printers, instead of the 4 in CMYK) The RGB space allows us to use all of them to best effect. 

Within the RGB colour model, there are many colour spaces. AdobeRGB and sRGB are the most common. You may have also need colour spaces such as ProPhoto and DCI-P3

You can see the difference in available colours in the example below.