Fission is the splitting of something into two or more parts. Scientists use this word most often when describing what happens inside atoms, the tiny particles that make up everything around us.

In nuclear fission, the nucleus (center) of a large atom breaks apart into smaller pieces, releasing energy. This process powers nuclear reactors that generate electricity. When a uranium atom undergoes fission, it splits and releases energy along with particles that can trigger other atoms to split, creating what scientists call a chain reaction.

You might hear this word outside of science too. When a political party splits into competing groups, someone might describe it as a fission of the party. In biology, certain simple organisms reproduce through binary fission, dividing themselves in two to create offspring.

Think of fission as the opposite of fusion (joining together). While fusion combines things, fission breaks them apart. The energy released when atoms undergo fission comes from the strong forces that normally hold the atom's nucleus together. When that nucleus splits, some of that binding energy is converted into heat and light, which is why nuclear fission produces such powerful results from such tiny amounts of material.