CMYK = Cyan, Magenta, Yellow, Black (K) — this is the four colors used in offset printing. Each color is traditionally printed on a separate color plate, with a different screen rotation. When layed or printed on top of each other it forms a dot pattern seen in printing. Think Lichtenstein prints where pictures are made up of dots. The dot pattern can be seen with a tool called a loupe.
RGB = Red Green Blue. Which is used in screen (web, presentations, LED light shows/projections or anything not printed on an offset printing press)
A spot color is custom mix of ink/color that is printed on it’s own color separation plate. It can also be a varnish or gloss plate.
More Jargon coming soon….