A dialect is a variety of language spoken by a particular group of people. It can also refer to a language subordinate in status to a dominant language, and is sometimes used to mean a vernacular language.
The more common usage of the term in English refers to a variety of a language that is a characteristic of a particular group of the language's speakers. The dialects or varieties of a particular language are closely related and, despite their differences, are most often largely mutually intelligible, especially if geographically close to one another in a dialect continuum. The term is applied most often to regional speech patterns, but a dialect may also be defined by other factors, such as social class or ethnicity. A dialect associated with a particular social class is called a sociolect; one associated with a particular ethnic group is an ethnolect; and a geographical or regional dialect is a regiolect (alternative terms include 'regionalect', 'geolect', and 'topolect'). Any variety of a given language can be classified as a "dialect", including standardized ones.
A second usage, which refers to colloquial settings, typically diglossic, exists in a few countries like Italy, such as dialetto, patois in France, much of East Central Europe, and the Philippines, and may carry a pejorative undertone and underlines the politically and socially subordinated status of an autochthonous non-national language to the country's official language(s). Dialects in this sense do not derive from a dominant language and are therefore not one of its varieties, though they may have evolved in a separate and parallel way. While they may be historically cognate with and share genetic roots in the same subfamily as the dominant national language and may, to a varying degree, share some mutual intelligibility with the latter, "dialects" under this second definition are separate languages from the standard or national language. Under this definition, the standard or national language would not itself be considered a dialect, as it is the dominant language in terms of linguistic prestige, social or political (e.g. official) status, predominance or prevalence, or all of the above. Dialect used this way implies a political connotation, often being used to refer to non-standardized "low-prestige" languages (regardless of their actual degree of distance from the national language) of limited geographic distribution, languages lacking institutional support, or even those considered to be "unsuitable for writing".
Occasionally, in a third usage, dialect refers to the unwritten or non-codified languages of developing countries or isolated areas, where the term "vernacular language" would be preferred by linguists.
Features that distinguish dialects from each other can be found in lexicon (vocabulary) and grammar (morphology, syntax) as well as in pronunciation (phonology, including prosody). In instances where the salient distinctions are only or mostly to be observed in pronunciation, the more specific term accent may be used instead of dialect. Differences that are largely concentrated in lexicon may be classified as creoles. When lexical differences are mostly concentrated in the specialized vocabulary of a profession or other organization, they are jargons. Differences in vocabulary that are deliberately cultivated to exclude outsiders or to serve as shibboleths are known as cryptolects or cant, and include slangs and argots. The particular speech patterns used by an individual are referred to as that person's idiolect.
Languages are classified as dialects based on linguistic distance. The dialects of a language with a writing system will operate at different degrees of distance from the standardized written form. Some dialects of a language are not mutually intelligible in spoken form, leading to debate as to whether they are regiolects or separate languages.
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