What is the Leakage Current of a Diode?

The leakage current of diode is the current that the diode will leak when a reverse voltage is applied to it.

Even though diodes are one-way devices, and they are only supposed to conduct current through them when they receive forward voltage (positive voltage to the anode), they will still conduct a small amount of current, called leakage current, when connected in reverse biased (positive voltage) to the cathode.

Below is a circuit of a diode connected in reverse biased:

For all basic purposes, leakage current is very small, and, thus, is normally negligible.

The leakage current only becomes very serious when the diode's reverse voltage reaches breakdown, which causes an avalanche of current to flow. But if reverse voltage is kept in a tolerable range, between 0 and breakdown, the current is very small.