Nuclear fusion is the process of combining two atomic nuclei to form a heavier nucleus. There are several synonyms for nuclear fusion, such as thermonuclear fusion, atomic fusion, and fusion reaction. Thermonuclear fusion refers to the fusion that takes place at extremely high temperatures, typically found in the core of stars. Atomic fusion, as the name suggests, refers to the fusion of atomic nuclei to form heavier nuclei. Fusion reaction is a technical term used to describe the process by which two atomic nuclei combine to form a heavier nucleus. These synonyms are often used interchangeably and refer to the process of combining atomic nuclei to release energy.