A formant is any of several prominent bands of frequency that determine the sound or phonetic quality of a vowel or consonant. Formants are the characteristic partials that identify vowels and consonants to the listener. They can be visualized on a spectrogram.
A formant is also a resonance of the vocal tract (see vocal resonance).
Formant bandwidth is the difference in frequency between the two half-power points on the slopes of a resonance curve.
Formant tuning is a boosting of vocal intensity when the fundamental frequency or one of its harmonics coincides exactly with a formant frequency.