The form of energy produced by nuclear reactions is known as "nuclear energy." This energy is released during nuclear fission, where the nucleus of an atom splits into smaller parts, or during nuclear fusion, where two light atomic nuclei combine to form a heavier nucleus. In fission, typically of uranium or plutonium isotopes, a significant amount of energy is generated, which is harnessed in nuclear reactors to produce electricity. In fusion, as seen in stars, including the Sun, immense amounts of energy are produced, but controlled fusion is still a subject of research for practical energy solutions.