Nuclear energy is the energy released during nuclear reactions, particularly:

1. Nuclear fission – the process of splitting a heavy atomic nucleus (like uranium-235 or plutonium-239) into two smaller nuclei, releasing a large amount of energy. This is the principle used in nuclear power plants to generate electricity.

2. Nuclear fusion – the process where two light atomic nuclei (like hydrogen isotopes) combine to form a heavier nucleus, releasing even more energy than fission. This is how the sun and other stars produce energy, and it's being researched for future power generation.

The energy released comes from the conversion of a small amount of mass into energy, as described by Einstein’s famous equation E=mc².

Nuclear energy is a low-carbon power source, meaning it produces minimal greenhouse gas emissions compared to fossil fuels, but it raises concerns like radioactive waste, nuclear accidents, and weapon proliferation.