a charged group of covalently bonded atoms

an ion An ion is an atom or group of atoms with a net electric charge

a tight group of atoms that carries a collective ionic charge and can participate as either the cation or anion in an ionic compound

an ion containing a number of atoms.

A polyatomic ion is an ion consisting of a molecule with covalently bonded atoms or of a metal complex that can be considered as acting as a single unit in the context of acid and base chemistry or in the formation of salts. The prefix poly- means many in Greek. Note, a polyatomic ion is also referred to in older works as a radical.