Formants are essentially fixed frequencies or resonances that occur due to the physical structure of the sound source. These frequencies produce the timbre and thus the specific sound of a voice or musical instrument. Formants can be specific frequency ranges, tones, vowels or sounds that are reproduced in a particularly intelligible manner. This is especially true for the human voice, which can change with vowels.
Formants are based on resonances and improve the intelligibility and identification of the human voice or an instrument because they can change with the vowels and have characteristics at certain resonant frequencies. The frequency enhancement is done with presence filters.