Fusion is the mechanism by which active stars are powered, releasing vast amounts of energy. The basis of the energy produced in the fusion of light elements is due to the interplay of two competing forces: the nuclear force, which draws protons and neutrons together and the Coulomb force, which repels each other by triggering protons.
Since the specific binding energy (binding energy per mass) of intermediate-mass nuclei with atomic numbers and atomic masses similar to 62Ni and 56Fe is greater than the nucleon-specific binding energy of very heavy nuclei, nuclear fission of heavy elements creates exploitable energy, so that energy is released.
Fusion power is a theoretical method of power generation that, by using heat from nuclear fusion reactions, will produce electricity. Two lighter atomic nuclei join in a fusion reaction to form a heavy nucleus, thus releasing energy. Devices meant to harness this power are referred to as fusion reactors.