An electronic component that only allows current to pass through it on one direction. Diodes have many applications. They are used to make rectifiers for power supplies and in many other applications where it’s important for current to flow in only one direction. They also come in a variety of physical configurations. The LED, or Light Emitting Diode, produces light (usually visible light, but not always) when current passes through it. In the domain of vacuum tubes the terms diode and rectifier are used interchangeably, however in solid state designs a rectifier can be a component or sub assembly made up of several solid state diodes. Either way the main purpose in that application is to change (or be a key step in changing) Alternating Current to Direct Current.