Answer:
Nuclear fission occurs when a heavy atom is divided or decomposed into lighter ones, and produce nuclear energy. An example of fission is the decomposition of uranium atoms to produce lighter elements such as barium. Fisition is a type of nuclear reaction, the other type of fusion that is the opposite of fission (in it light elements combine to form a heavier one).
Nuclear fission occur or is used in the manufacture of nuclear bombs and also in nuclear power plants to generate electricity.