Signature

A specification of the nonlogical vocabulary of a formal language: a set of symbol declarations including constant symbols, function symbols with arities, and relation (predicate) symbols with arities that determine the syntactic building blocks available to form terms and atomic formulas.

The signature (or inertia) of a symmetric bilinear form or quadratic form over the reals is the ordered triple (p, n, z) giving the numbers of positive, negative, and zero eigenvalues of any representing symmetric matrix, describing its definiteness pattern.