A light-emitting-diode (LED) is a semiconductor diode that emits light when an electric current is applied in the forward direction of the device, as in the simple LED circuit.
Light color is associated with the light wavelength. The dominant wavelength and therewith the color of the light depends on the material of the semiconductor device.
Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass.
Simply put, RGB stands for the three different types of LEDs within a color changing fixture; Red, Green and Blue. RGB fixtures use the additive color system to combine emitted lights in order to create the sensation of a range of colors.