Question

What is a rectifier and filter?

Answer 1

Rectifier is a device which converts AC current into DC by allowing the current to flow only in a specified direction.
Filters are used to remove unwanted frequency components from the signals.Electronic filters are of different types.

Answer 2

Rectifier is a circuit that makes the current flow through the load or at the output in one direction only.

Or a rectifier is a circuit which inverts the negative half wave of a sinusoidal voltage signal.

Its helps to convert AC to DC wave.

You know that a signal can have composition of different frequency components ie. it may have more than one sin or cosine terms.

So a filter is a circuit which can filter out what ever kind of frequencies you don't need in a signal. Eg. If you only want only high frequencies, a high pass filter will help you remove lower frequency components.