And yes, the AOD stands for "Applications of Diodes" & we're gonna use that for the rest of the apps as well.

Diodes are used in rectifiers which are devices that convert an AC to a DC signal, not a pure dc signal though... And as a matter of fact, the only source of pure DC is a battery.

And this process of converting AC to DC is called rectification. Consider a simply sine wave as the input from an AC source. Then the following summarizes the overall process of rectification...

So, there is no output for the negative half as the diode is in the reverse bias condition(considered OFF). Also, the circuit we use here is just what the half wave rectifier really is.

Now, considering the two halves collectively, we get an output signal like so...

Notice here that the peaks of the positive cycle appear at equal distances, and this distance is same for the input & the output signal. Hence, the frequency of the signal does not change.

(f_in=f_out)

Getting into the mathematical view of things, we can now calculate the RMS & Average values of the voltage for our new output signal.