What is rectification and rectifier? Why is a $p-n$ junction diode used as a rectifier?

(N/A) Rectification is the process of converting alternating current $(AC)$ into direct current $(DC)$.
$A$ device that performs this process is called a rectifier.
$A$ $p-n$ junction diode is used as a rectifier because it exhibits unidirectional current flow properties.
When the diode is forward-biased,it offers very low resistance and allows current to flow.
When the diode is reverse-biased,it offers very high resistance and blocks the current flow.
This property allows the diode to conduct only during the positive half-cycle of the $AC$ input,effectively converting it into a pulsating $DC$ output.