The term for a type of decay that involves the emission of a proton or neutron from an atomic nucleus is beta decay. In this process, a neutron is transformed into a proton, or vice versa, leading to the emission of beta particles (electrons or positrons). This transformation alters the atomic number and can change the element into a different isotope or a entirely new element. Beta decay is a common form of radioactive decay observed in unstable isotopes, contributing to the decay chain in nuclear reactions.