Peter was attacked by a black cat when he was young. Due to this, he developed a fear of cats. A few years later, his parents got him a black kitten, and his fear gradually extinguished. On his way to work one day, he saw a black cat running toward him and felt his old fear resurfacing. In this scenario, the recurrence of Peter's fear of cats is known as .

spontaneous recovery

Explanation:

Spontaneous recovery is a phenomenon that involves suddenly displaying a behavior that was thought to be extinct.

Spontaneous recovery can be defined as the reappearance of the conditioned response after a rest period or period of lessened response

After a conditioned response has been extinguished, spontaneous recovery may gradually increase as time passes. However, the returned response will generally not be the same strength as the original response unless additional conditioned takes place.

For example, In this context , Peter fear of cats  became lessened due to the fact has a black kitten which his parents gave him, but upon sighting a black cat running towards him he developed that old fear which was gradually reducing.This  can be described as a spontaneous recovery