The ions which have more than one ions!!
Ions which contains more than one atom

Polyatomic ions are the group of atoms which carry either positive charge (cations) or negative charge (anions). For example,(i) Carbonate ion (CO3)2- (ii) Nitrate ion (NO3)- (iii) Ammonium ion (NH4)+ (iv) Phosphate ion (PO4)3-.