n. 1. (Logic) an assignment to a first-order language of a non-empty set (the universe) of which the elements are individuals, and of functions, predicates, and constants in that universe to the corresponding symbols of the language with the exception of identity. A structure for a theory in which its non-logical axioms are true is a model for the theory. 2. a set endowed with some prescribed functions, predicates, or relations, usually of an algebraic nature. Compare space.