In applied linguistics, an error is an unintended deviation from the immanent rules of a language variety made by a second language learner. Such errors result from the learner's lack of knowledge of the correct rules of the target language variety. A significant distinction is generally made between errors and mistakes which are not treated the same from a linguistic viewpoint. The study of learners' errors has been the main area of investigation by linguists in the history of second-language acquisition research.
