"RGB" means Red, Green, Blue: the colors you can control per bulb to create a million different colors!
A smart pixel light ribbon or smart pixel light string means every pixel is individually controllable. 50 sections on your smart pixel ribbon? Each section can be any color. 50 lights on your smart pixel string? Each light can be any color. A dumb RGB device (like a flood light) can have its one light bulb turn any color you wish.