What does the term filter in an audio equalizer mean?

Answer 1

A filter is a circuit which can pass a certain range of frequencies.

There are several types.

A low-pass filter passes frequencies below a certain figure.

A high-pass one passes frequencies above a certain figure.

A band-pass one passes frequencies between two figures

A band-reject filter passes frequencies below a certain figure and above another, rejecting the others.

A notch filter is similar to the band-reject but is very narrow so it rejects a specific frequency.

An all-pass filter passes all frequencies but shifts their phase.

An audio equaliser is a group of filters with pass-bands adjacent to each other.
This means that you can fiddle about with the frequency response of the audio system and make it sound unnatural.

The recording engineer and other people who are involved in the recording chain go to great lengths to ensure the recording is as faithful to the original as is reasonably possible. Why someone should then want to mess around with an equaliser beats me.