:Formant transition:

Pronunciation GBː ˈfɔːmənt, GA: ˈfɔrmənt

The rapid change in frequency of a formant for a vowel immediately before or after a consonant. The F2 transition is a very important acoustic cue to the place of articulation of a consonant. The F1 transition signals information about the manner of articulation of a consonant.

A wideband spectrogram of the utterance aba, showing formant transitions.
The vertical blue lines enclose the steady state portion of the second vowel.