Aversion therapy refers to the condition ing technique for attempting to eliminate unwanted behaviour by pairing an unpleasant (aversive) stimulus with the behaviour—for example, inducing nausea when alcohol is consumed. A form of behavior therapy in which the undesirable response leads to an aversive stimulus (e.g., the patient shocks herself every time she reaches for a cigarette).
Other /More definition:
Aversion therapy refers to a controversial type of treatment in which an undesired behavior is followed consistently by an unpleasant consequence, thus decreasing the strength of the behavior over time; suppressing an undesirable response by associating it with aversive (painful or uncomfortable) stimuli.
It is a type of behavioral therapy, based on classical conditioning techniques, that uses some aversive stimulus to counter-condition the patient's response.