The question belongs to the series of inter-related questions and arguments that are somehow related to the Parallel Universe Theories. There are multiple point-of-views when it comes to defining the Difference Between Parallel Universe and Multiverse. Let's discuss the two concepts of Parallel Universe and Alternate Universe in the first place.

Parallel Universe: The concept of Parallel Universe stands for the theory that arises from the concept of big-bang theory. Big bang theory describes the existence of our universe and the probable start of life on earth. It describes the circumstances that lead to the formation of Earth and other planets in our solar system. The arguments lead to the formation of parallel universe theory. As, the events that lead to the formation of the solar system should keep happening now and then, as scientific knowledge doesn't have any evidence of the formation of the solar system under a controlled environment, and it all happened accidentally or as a result of "sequence" or "continuous events."