A term that originally referred to those elements with spherically shaped nuclei that would reside on the “island of stability.” More recently, the term “superheavy elements” has been widened to include heavy nuclei whose existence is due to the nuclear shell effect. In this widened definition, therefore, elements with atomic number Z ≥ 104 are generally considered to be superheavy (which also coincides with the beginning of the transactinide elements).