The return of the libido on to phantasy is an intermediate step on the way to symptom-formation which well deserves a special designation. C. G. Jung has coined for it the very appropriate name of INTROVERSION
Freud identifies the libido’s regression onto phantasy as the pivotal mechanism in symptom-formation, simultaneously marking the conceptual boundary between his use of ‘introversion’ and Jung’s broader application of the term.
, Introductory Lectures on Psycho-Analysis, 1917thesis