"Fusion reaction" refers to the process of combining two atomic nuclei into a single, heavier nucleus, releasing a vast amount of energy. There are several synonyms for this term, including thermonuclear reaction, nuclear fusion, and fusion event. Thermochemistry and thermonuclear fusion reactions are other words to describe this reaction. Additionally, fusion energy, nuclear fusion energy, and fusion power describe the energy that is produced by the fusion reaction. The process can occur naturally in stars, as well as artificially in reactors, and understanding its mechanics is crucial to the development of clean, sustainable energy sources for the future.