diode

A type of electronic component that is normally intended to conduct current in only one direction. They are a P-N junction device with non-linear characteristics. They were also the first semiconductor electronic devices created. A standard P-N Diode has two sides the Cathode and Anode (a white band on the device signifies the cathode).

The Symbol for a diode is a triangle with a bar on one end (the cathode side), modifiers are added to signify special types of diodes.

Diodes are generally used to rectify power (Turn AC into DC) or to direct current in the way intended. Various kinds of Diodes are used for other functions as well. The Cathode points in the direction that current is to be allowed to flow.

There are to primary forms of power rectification half-wave and full wave. A full-wave rectifier is a series of four (4) diodes in a wheatstone bridge configuration.

There are many types of diodes and here is as brief description of most:

Light Emitting Diodes (LEDs) are used to create light.
Zener Diodes are used to regulate voltage (Reverse biased).
Tunnel Diodes are used to generate RF oscillations.
Varactor Diodes are used to electronically tune radio/tv receivers.
Photodiodes are used to detect light (light sensors, photocells, remote controller receivers).
(SCRs) Silicon Controlled Rectifiers are interesting diode devices commonly seen in dimmers.