 A schema (plural: schemata, or schemas), also known as a scheme (plural: schemes), is a linguistic “template”, “frame”, or “pattern” together with a rule for using it to specify a potentially infinite multitude of phrases, sentences, or arguments, which are called instances of the schema. Schemas are used in logic to specify rules of inference, in mathematics to describe theories with infinitely many axioms, and in semantics to give adequacy conditions for definitions of truth.