A nonstandard dialect is a dialect

Dialect

The term dialect is used in two distinct ways, even by linguists. One usage refers to a variety of a language that is a characteristic of a particular group of the language's speakers. The term is applied most often to regional speech patterns, but a dialect may also be defined by other factors,...

 that does not have the institutional support or sanction that a standardized dialect

Standard language

A standard language is a language variety used by a group of people in their public discourse. Alternatively, varieties become standard by undergoing a process of standardization, during which it is organized for description in grammars and dictionaries and encoded in such reference works...

 has.

Like any dialect, a nonstandard dialect has its own vocabulary

Vocabulary

A person's vocabulary is the set of words within a language that are familiar to that person. A vocabulary usually develops with age, and serves as a useful and fundamental tool for communication and acquiring knowledge...

 and an internally consistent grammar

Grammar

In linguistics, grammar is the set of structural rules that govern the composition of clauses, phrases, and words in any given natural language. The term refers also to the study of such rules, and this field includes morphology, syntax, and phonology, often complemented by phonetics, semantics,...

 and syntax

Syntax

In linguistics, syntax is the study of the principles and rules for constructing phrases and sentences in natural languages....

; and it may be spoken using a variety of accent

Accent (linguistics)

In linguistics, an accent is a manner of pronunciation peculiar to a particular individual, location, or nation.An accent may identify the locality in which its speakers reside , the socio-economic status of its speakers, their ethnicity, their caste or social class, their first language In...

s. Describing a dialect as "nonstandard" is not to imply that the dialect is incorrect or inferior. Also prestige dialect

Prestige dialect

In sociolinguistics, prestige describes the level of respect accorded to a language or dialect as compared to that of other languages or dialects in a speech community. The concept of prestige in sociolinguistics is closely related to that of prestige or class within a society...

s may be non-standard.

As a border-case, a nonstandard dialect may even have its own written form, although it's then to be assumed that the orthography is unstable and/or unsanctioned, and that it is not orderly supported by governmental or educational institutions. When used in quotes and as a contrastive feature in literature

Literature

Literature is the art of written works, and is not bound to published sources...

, the term eye dialect

Eye dialect

Eye dialect is the use of non-standard spelling for speech to draw attention to pronunciation. The term was originally coined by George P. Krapp to refer to the literary technique of using non-standard spelling that implies a pronunciation of the given word that is actually standard, such as...

may be used for nonstandard phonemic spelling.

It is uncommon in written texts unless the text is dialect poetry, etc.