text: IUPAC nomenclature has extensive rules to cover the naming of cyclic structures, both as core structures, and as substituents appended to alicyclic structures. The term macrocycle is used when a ring-containing compound has a ring of 12 or more atoms. The term polycyclic is used when more than one ring appears in a single molecule. Naphthalene is formally a polycyclic compound, but is more specifically named as a  bicyclic compound. Several examples of macrocyclic and polycyclic structures are given in the final gallery below.
  The atoms that are part of the ring structure are called annular atoms.