The salts that contain more than one cation or anion are known as 

The salts that contain more than one cation or anion are known as double salts. 
Mohr's salt is a two-salt mixture that contains more than one simple salt. In aqueous solutions, it undergoes complete dissociation. 

Alum and Tutton's salts are examples of double salts. Potassium sodium tartrate,also known as Rochelle salt (KNaC₄H₄O₆·4H₂O) is also an example of double salt.