Definition:Radioactive Decay/Stable

Definition
An isotope of a chemical element which is not subject to radioactive decay is described as stable.

It follows that the half-life of such an element is infinite.

Also known as
The term stable element is sometimes seen, but this is inaccurate and misleading.

All elements have isotopes which are radioactive, and most have isotopes which are stable.

Thus it is accurate only to refer to stable isotopes or radioactive isotopes, although note that the term radioactive element can always be used for elements none of whose isotopes are stable.