The act or process of reinforcing or the state of being reinforced. Something that reinforces. Additional personnel or equipment sent to support a military action. Often used in the plural. Psychology The occurrence or experimental introduction of an unconditioned stimulus along with a conditioned stimulus. Psychology The strengthening of a conditioned response by such means. Psychology An event, a circumstance, or a condition that increases the likelihood that a given response will recur in a situation like that in which the reinforcing condition originally occurred.