Reinforcement is a term in operant conditioning
Operant conditioning
Operant conditioning is a form of psychological learning during which an individual modifies the occurrence and form of its own behavior due to the association of the behavior with a stimulus...

 and behavior analysis for the process of increasing the rate
In mathematics, a rate is a ratio between two measurements, often with different units. If the unit or quantity in respect of which something is changing is not specified, usually the rate is per unit time. However, a rate of change can be specified per unit time, or per unit of length or mass or...

 or probability of a behavior
Behavior or behaviour refers to the actions and mannerisms made by organisms, systems, or artificial entities in conjunction with its environment, which includes the other systems or organisms around as well as the physical environment...

 (e.g., pulling a lever more frequently) in the form of a "response" by the delivery or emergence of a stimulus
Stimulus (psychology)
In psychology, stimuli are energy patterns which are registered by the senses. In behaviorism and related stimulus–response theories, stimuli constitute the basis for behavior, whereas in perceptual psychology they constitute the basis for perception.In the second half of the 19th century, the...

 (e.g. a candy) immediately or shortly after performing the behavior.

The response strength is assessed by measuring frequency, duration, latency, accuracy, and/or persistence of the response after reinforcement stops.