1. A sudden collapse, as of an evacuated vessel, in which there is a bursting inward rather than outward as in an explosion. 2. A type of behavior therapy, similar to flooding, during which the patient is given massive exposure to extreme anxiety-arousing stimuli by being asked to describe, and thus relive in imagination, those life events or situations typically producing these overwhelming emotional reactions. As the patient does so, the therapist attempts to extinguish the future influence of such unconscious material over the patient's behavior and feelings, and previous avoidance responses to the stimuli are replaced by more appropriate responses.