What is the unidirectional conductivity of a diode?

What is the unidirectional conductivity of a diode?

The definition of unidirectional conductivity of a  diode: The current flowing through the  diode can only flow from the positive pole to the negative pole, and cannot flow from the negative pole to the positive pole, which is called the positive conductivity of the  diode.

The significance of  diode unidirectional conductivity to map reading: the triangle in the diode Electronic symbol vividly represents the current flow direction. Using the prompt function of this Electronic symbol, it is convenient to know the current flow direction in the circuit when analyzing the circuit. When analyzing the working principle of diodes in DC circuits, because the voltage that causes the diode to conduct can only be applied from the positive pole to the negative pole, when analyzing where this voltage is applied, one can start from the positive pole of the diode and search for the direction of DC voltage supply.

To make the diode conductive, a forward bias voltage must be applied to the diode. If the applied voltage is not large enough, the diode can only be in a micro conductive state: if the applied reverse voltage (negative voltage is higher than positive voltage), the  diode cannot conduct and is in a cut-off state.