A light emitting diode (LED) is a special type of diode that emits light when current flows through it.
The LED is just one type of a larger family of components known as the diode. Diodes, including LEDs, have two leads, a positive anode and a negative cathode.
A good way to remember which is which is to think about grades. Getting an A in class is more positive than a C, and for many, getting a C is a negative for their overall GPA. Components that have positive and negative leads are known as having polarity and can only be inserted into a circuit in one direction. If you place an LED in a circuit backwards, it won’t illuminate — that’s because it won’t let current flow through it.
A Colorful History!
LEDs come in all different colors, but surprisingly white LEDs are usually not actually white. Here's a full breakdown on the History of White LEDs.