(linguistics, strict sense) A lect (often a regional or minority language) as part of a group or family of languages, especially if they are viewed as a single language, or if contrasted with a standardized idiom that is considered the 'true' form of the language (for example, Cantonese as contrasted with Mandarin Chinese or Bavarian as contrasted with Standard German).

(linguistics, broad sense) A variety of a language that is characteristic of a particular area, community, or social group, differing from other varieties of the same language in relatively minor ways as regards grammar, phonology, and lexicon.

(derogatory) Language that is perceived as substandard or wrong.

(colloquial, offensive) A language existing only in an oral or non-standardized form, especially a language spoken in a developing country or an isolated region.

(computing, programming) A variant of a non-standardized programming language.

(ornithology) A variant form of the vocalizations of a bird species restricted to a certain area or population.