CMYK
The four ink colors used in print: cyan, magenta, yellow and black.
Screens mix light in red, green and blue (RGB). Printing mixes ink in cyan, magenta, yellow and black (CMYK).
Some very bright screen colors, like neon greens and electric blues, can't be matched exactly in ink and print a little calmer. Converting to CMYK before you export lets you see that on screen first.
Go deeper