The name of the polyatomic ion ClO2- is chlorite.
This is one of the oxyanions of chlorine, which are polyatomic ions that contain oxygen and have different numbers of oxygen atoms.
The names and formulas of the oxyanions of chlorine are:
hypochlorite: ClO^-
chlorite: ClO2^-
chlorate: ClO3^-
perchlorate: ClO4^-