The customary manner in which a language (or a form of a language) is spoken or written WordNet 3.0 & Open English WordNet

The usage of a language is the ways in which its written and spoken variations are routinely employed by its speakers; that is, it refers to "the collective habits of a language's native speakers", as opposed to idealized models of how a language works or in the abstract. Wikipedia

Manner in which a language is actually used, e.g., regionalisms, colloquialism, jargon, etc., and as opposed to formal models or prescriptive ideals Wikidata