Ions that have the same (for lack of a better word) absolute
value of charge.
Meaning 1+ and 1- ions will combine in a 1:1 ration (Na+ + Cl-
--> NaCl), as will 2+ ions with 2- ions (Mg2+ + SO42- -->
MgSO4) and 3+ ions with 3- ions (Al3+ + N3- --> AlN)