Double beta decay is a rare type of radioactive decay in which a nucleus emits two beta particles simultaneously. This process occurs in certain isotopes that are energetically allowed to decay by emitting two electrons and two neutrinos. It is a unique way for unstable nuclei to reach a more stable state. This decay is significant in the study of neutrinos and lepton number violation, as it can provide insights into the properties of these fundamental particles. Observing double beta decay can help scientists understand the nature of dark matter and the overall behavior of matter in the universe.