Final answer:
The stimulus which is removed after a response to strengthen that response is known as a negative reinforcer, a concept in operant conditioning that signals the removal of an unpleasant stimulus to increase the likelihood of a behavior's recurrence.
Step-by-step explanation:
Understanding Operant Conditioning
Any stimulus that, when removed after a response, strengthens the response is called a negative reinforcer. This is because the stimulus (which is usually seen as unpleasant or undesirable) is taken away or removed after the occurrence of a behavior, thus making the behavior more likely to happen again in the future. It is important to note that negative does not imply bad in this context, but rather the removal of a stimulus as opposed to the addition which would be indicated by the term positive.
Reinforcement in either form aims to increase a behavior, whereas punishment is designed to decrease a behavior. For example, in horse training, the pressure applied by the reins or legs is removed when the horse performs the desired behavior, thus the removal of pressure acts as a negative reinforcer, increasing the likelihood of the horse's compliance in future.