Biasing
Bias or biasing as a method of establishing a set of currents or
voltages at different points of an electronic circuit to establish proper
operating conditions within an electronic component. Although this is a
simplified version of the answer, it is still fundamentally correct.
Furthermore, with biasing, resides the two types of biasing, forward bias and
reverse bias.
A diode (PN junction) functions much like a one-way highway since it
allows the flow of current more easily in one direction than the other. In
summary, a diode typically conducts current in one direction, and the
voltage they apply follows a described forward biasing orientation. However,
when the voltage moves in the reverse direction, we refer to this orientation
as reverse bias. Also, when in reverse bias, a standard PN junction diode will
typically inhibit or block the
flow of current, almost like an
electronic version of a check valve.

Forward Bias: This bias condition incorporates the connecting of a positive
voltage potential to the P-type material and a negative to the N-type
material across the diode, thus decreasing the width of the diode.

Reverse Bias: In contrast, this biasing condition involves the connection of
a negative voltage potential to the P-type material and a positive to the Ntype material across the diode, thus increasing the width of the diode.

Zero Bias: This is a bias condition in which there is no external voltage
potential applied to the diode.
Forward Bias vs. Reverse Bias
In a standard diode, forward biasing occurs when the voltage across a diode
permits the natural flow of current, whereas reverse biasing denotes a
voltage across the diode in the opposite direction.
However, the voltage present across a diode during reverse biasing does not
produce any significant flow of current. Furthermore, this particular
characteristic is beneficial for changing alternating current (AC) into direct
current (DC).
There are a variety of other uses for this characteristic, including electronic
signal control.