Spontaneous recovery is a term associated with learning and conditioning. Specifically, spontaneous recovery is the reappearance of a response (a Conditioned Response; CR) that had been extinguished. The recovery can occur after a period of non-exposure to the Conditioned Stimulus (CS). It is called spontaneous because the response seems to reappear out of nowhere. Let's look at an example. Let's say I condition (teach/train) a rat to press a lever whenever I ring a bell. Then I teach the rat to press the lever when I flash a light and not when I ring the bell. Once I've accomplished this, we can say that the first conditioned response (pressing the lever when I ring the bell) has been extinguished. But then one day, the rat starts to press the lever when I ring the bell and not when I flash the light. In this situation, there was spontaneous recovery of the response that was previously extinguished.