How is a rectifier diode defined?

A rectifier diode is defined primarily by its ability to allow current to flow in one direction while providing high resistance to current flow in the opposite direction. This property is fundamental to the function of rectifier diodes, which are widely used in converting alternating current (AC) to direct current (DC).

The characteristic of high opposition in the reverse direction is crucial because it prevents current from flowing the wrong way, making the diode effective for applications such as power supply circuits, where a stable DC output is necessary for the operation of electronic devices. This directional behavior enables rectification, which is the process of converting AC, which can vary in direction and voltage, to DC, suited for most electronic applications.

In contrast, other options do not align with the defining characteristics of a rectifier diode. Conducting equally in both directions, allowing for variable current flow, and amplifying signals do not describe the essential, directional conduction feature unique to rectifier diodes.