Nuclear fusion and fission release energy by converting mass into energy, as described by Einstein's equation E=mc². Fission occurs in heavy nuclei like uranium and involves splitting the nucleus, which releases energy and additional neutrons, resulting in a mass defect. Fusion, on the other hand, involves combining light nuclei, such as hydrogen, where energy is released due to the loss of mass during the process. Binding energy plays a crucial role, as it is the energy required to separate nucleons from the nucleus, and the energy dynamics differ between fusion and fission based on the atomic number of the elements involved. Overall, both processes are fundamentally linked to changes in mass and energy release.