1) The procedure of providing consequences for a behavior that increase or maintain the frequency of that behavior.

2) The operation of immediately following responses with consequences that result in an increase in the occurrence of the response class.

3) A process in which a behavior is strengthened (i.e., the behavior's frequency, rate, duration, intensity, or other dimensions increase or persist) as a function of an event that occurs as a consequence of, or contingent on, the response. Reinforcement may occur naturally or be planned. It is defined solely by its function of increasing or maintaining behavior. Two basic reinforcement procedures are discussed in this book. positive reinforcement and negative reinforcement. Both increase or maintain behavior.

4) Any event which maintains or increases the probability of the response it follows. Either the presentation of a positive reinforcer or the removal or reduction of an aversive stimulus.

5) The response-produced presentation of positive reinforcers or termination of negative reinforcers (or the increase or maintenance of responding resulting from this operation). Reinforcers are stimuli (e.g., food); reinforcement is an operation (e.g., presentation of food) or a process. The operation reinforces responses, not organisms; organisms are sometimes said to be rewarded, but this term often implies effects of stimuli other than reinforcing effects. Earlier in its history, reinforcement was also applied to presentations of the US in respondent conditioning, but that usage is now unusual. (Catania) A stimulus is a positive reinforcer if its presentation increases the likelihood of responses that produce it, or a negative reinforcer if its removal increases the likelihood of responses that terminate or postpone it. The distinction is significant mainly when responses produced by the reinforcer can compete with the reinforced response (e.g., reinforcement by heat of a rat's lever presses in the cold is more likely to be called negative reinforcement by removal of cold than positive reinforcement by presentation of heat because cold produces huddling and shivering that compete with lever-pressing).

6) An increase in the rate of operant behavior as a function of its consequences. Also, the procedure of presenting a reinforcing consequence when a response occurs.

7) When a stimulus follows a performance, reinforcement has occurred.