Diode, electronic component, a device with two electrodes that allows current to flow in only one direction; many uses are for its rectifying function. The Varicap Diode is used as an electronically adjustable capacitor. The directivity of current present in most diodes is often referred to as "Rectifying". The most common function of a diode is to allow current to flow in only one direction (called forward bias) and to block it in the reverse direction (called reverse bias). Therefore, the diode can be thought of as the electronic version of the current check valve.