A primary reinforcer is a stimulus that is naturally reinforcing to an individual. Primary reinforcers are stimuli that are essential for the survival and well-being of an organism, such as food, water, and shelter. They are reinforcing because they satisfy basic physiological needs, such as hunger, thirst, and the need for warmth and safety. Primary reinforcers are often used in operant conditioning, which is a type of learning that occurs through the association of stimuli and responses. Primary reinforcers are effective at reinforcing behavior because they are innately reinforcing, and do not require any previous learning or conditioning to be effective.