What is the process by which hydrogen is converted into helium in the Sun’s core, producing energy?

Nuclear fusion is the process where hydrogen nuclei combine to form helium, releasing tremendous energy. This is the primary source of the Sun's energy, keeping it shining and providing heat.
Nuclear fission is splitting a large nucleus into smaller nuclei, which does not occur in the Sun.
Gravitational collapse refers to the contraction of matter under gravity, significant during the formation of stars.
Radioactive decay is the breakdown of unstable nuclei.