LED means Light Emitting Diode
An LED is a semiconductor that emits light when electric current passes through it.
The emission of light depends on electrons flowing through the junction between P and N regions; when an electron from the N region passes the junction and recombines with a hole in the P region, its energy is radiated as a light pulse.
The color of that light
depends on the used
it can be red, amber, green or blue.