- Quantifier (logic) (Wikipedia)
In logic, a quantifier is an operator that specifies how many individuals in the domain of discourse satisfy an open formula. For instance, the universal quantifier ∀ in the first order formula ∀xP(x) expresses that everything in the domain satisfies the property denoted by P. On the other hand, the existential quantifier ∃ in the formula ∃xP(x) expresses that there exists something in the domain which satisfies that property. A formula where a quantifier takes widest scope is called a quantified formula. A quantified formula must contain a bound variable and a subformula specifying a property of the referent of that variable.