Answer and Explanation:
A nuclear fusion reaction is when two atomic nuclei combine, which creates a much bigger and heavier nucleus. When this fusion is preformed, it releases high energy. After this process is formed, the sum of the two nuclei creating the nucleus has less mass than the original two nuclei alone.
Typically, this form of fusion isn't really able to happen on Earth. This form of fusion is something that is most commonly known to happen in space, to the Sun and the stars. Because of the high energy reaction after the process that is released, this is something that fits a reaction for the Sun and stars quite well.
I hope that this helps.
