In logic quantifiers are prefixes that tell us what range of things are covered by the succeeding logical formula. The most common are "forall", denoted by an upside-down A -- ∀, and "exists", denoted by a back-to-front E -- ∃. Temporal logics also have opertairs to talk about time such as "always" or "eventually", and in general modal logics have additional quantifiers to talk about different kinds of worlds, such as belief states.
Used on Chap. 2: page 21