LED (Light Emitting Diode) is a special diode that emits light when an electric voltage is applied to it. It is common electronic component that is being used in devices like TV, computer, etc. generally for indicating purpose. They are available in various colors like red, yellow, green etc.
There are two leads of an LED that are used to supply input voltage. The longer lead is positive and known as ‘Post’, and the smaller is negative known as ‘Anvil’ as shown in the image above.