Question

the term radio activity ... editing​

Answer 1

Radioactive decay is the process by which an unstable atomic nucleus loses .... Radioactive substances[edit] ... The International System of Units (SI) unit of radioactive activity

Answer 2

Radioactive decay (also known as nuclear decay, radioactivity or nuclear radiation) is the process by which an unstable atomic nucleus loses energy (in terms of mass in its rest frame) by emitting radiation, such as an alpha particle, beta particle with neutrino or only a neutrino in the case of electron capture, or a gamma ray or electron in the case of internal conversion. A material containing such unstable nuclei is considered radioactive. Certain highly excited short-lived nuclear states can decay through neutron emission, or more rarely, proton emission.