An acidic salt is formed in the reaction of neutralization between a strong acid and a weak base. For example, AlCl₃ is a product of neutralization reaction between HCl and Al(OH)₃. HCl is a strong acid and Al(OH)₃ is a weak base. Hence, AlCl₃ is an acidic salt.

Another way to look at this: an acidic salt is made of a cation, which is a weak Bronstead-Lowry acid, and an anion, which is a Bronstead-Lowry base of negligible strenth (not a base). For example, Al³⁺ is a weak acid. Cl^- has negligible strength as a base (not a base). Hence, AlCl₃ is an acidic salt.

Other common examples are NH₄Cl, NH₂(CH₂CH₃)₂Br, etc.