What do you mean by zener diode?

Question

What do you mean by zener diode?

Answer 1

A Zener Diode is a special kind of diode which permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value - the breakdown voltage known as the Zener voltage.

Answer 2

A zener diode normally only allows current flow in only one direction (like a normal diode).  However, if a high enough voltage is applied in the reverse direction, called the breakdown voltage, it will allow current to flow in the reverse direction.

A regular diode also has breakdown voltage where this will happen, but it is usually much higher and once exceded the normal diode is ruined.