Usus (Latin: usus — usage; long-established rule, practice, custom) is the common usage of linguistic units (words, idioms, forms) in a particular speech community.[1][2][3] It may be used as one of the criteria of laying out prescriptive norms for standard language usage.[4]

Usus can be contrasted with both low-frequency usage and codified standard usage. The term is used to designate usage that has widespread or significant acceptance among speakers of a language, regardless of its conformity to the sanctioned standard language norms.[1]

Usus was a crucial term in the research of Danish linguists Otto Jespersen and Louis Hjelmslev.[5]