Jitter

Fluctuations in pitch. Excessive jitter makes a voice sound creaky (see creaky voice).

Mean absolute jitter is the mean absolute difference between sequential vocal periods measured during a sustained phonations (in seconds or milliseconds). However, absolute jitter is influenced by the mean fundamental frequency of the speaker. For this reason, relative jitter measures have been proposed. Mean jitter factor is the mean absolute difference between sequential vocal fundamental frequencies (in Hertz) divided by the mean frequency of the phonation.

Link
Utrecht Lexicon of Linguistics Audiodemonstration jitter