(mathematics, logic) Denoting the second in a numerical sequence of models, languages, relationships, forms of logical discourse etc. / Of secondary importance.

a stream formed by the confluence of two first order streams, or of a first order stream and a second order stream

A formal system which extends first-order logic by allowing quantification over relations between members of the universe.

plural of second-order logic

(military) A factor that may eventually lead to a direct military threat.

plural of second order stream

(logic) A formal deductive system which extends first-order logic by the ability to quantify over unary predicates over individual members of the universe of discourse.

plural of monadic second-order logic