Forward biasing is when voltage is applied across a P-N junction in the forward direction, according to About.com. A reverse bias does just as the name suggests, reversing the flow of the current through the diode.
Forward and reverse biasing describe the ways in which current flows through P-N junctions. These junctions only allow current to flow in one direction. When the current flows in the forward direction, or forward bias, then the electrons from the N-type region combine with the holes that are located in the P-type region. On the other hand, when the current is reversed, or put it in reverse bias, then the electrons and holes are forced apart, which prevents the current from moving across the junction.
Today, the components of both forward and reverse biasing are commonly used to create transistors, which are designed to control the way electrons move in a device. A transistor does not just determine how electrons move; it also determines how much current runs through it. Through using a combination of reverse and forward biasing, a transistor can both greatly increase the amount of electrons that runs through an item and instantly stop the electrons from moving through it entirely.