If a conditioned stimulus (cs) is presented without further pairings with the unconditioned stimulus (us), the cs will gradually lose its capacity to elicit the conditioned response. this is the definition of:

This is the definition of respose extinction.

Explanation:

For example, you taught your dog to sit everytime you grab his leash to go for a walk. Over time you started to let him run in the backyard to exercise, and you show him the leash to just call his attention. One day you grab the leash to take him for a walk, and you realize he does not sit anymore at the stimulus. This is a case of response extinction.        

all the above is what i would say