Not conforming to the usual or expected standards or norms.
The nonstandard design of the building made it stand out in the neighborhood.
Not following the accepted rules of grammar or usage in a language.
His nonstandard use of English was evident in his informal speech.
(Mathematics, Logic) Relating to or employing a formal system, model, or analysis that differs from the conventional (standard) one, especially by using infinitesimals.
Nonstandard models of arithmetic allow mathematicians to explore properties that cannot be proved in the standard system.