commitment [L, committere, to entrust] , 1. the placement or confinement of an individual in a specialized hospital or other institutional facility. See also institutionalize. 2. the legal procedure of admitting a mentally ill person to an institution for psychiatric treatment. The process varies from state to state but usually involves judicial or court action based on medical evidence certifying that the person is mentally ill. See also certification. 3. a pledge or contract to fulfill some obligation or agreement, used especially in some forms of psychotherapy or marriage counseling.