APA Dictionary of Psychology

the class of responses whose probability is changed by the imposition of an operant contingency. For example, lever presses with a force greater than 0.2 N may be required for reinforcement. Presses with forces greater than 0.2 N will increase in frequency, as will the frequency of presses just (but not far) below that value. These latter presses are part of the functional operant class. Compare descriptive operant.