A nonstandard dialect of a language is a dialect of a language that does not have the institutional support or sanction that a standardized dialect has.
A nonstandard dialect has its own vocabulary and an internally consistent grammar and syntax. A nonstandard dialect, like a standard dialect, may be spoken using a variety of accents. A nonstandard dialect may even have its own written form.
Describing a dialect as "nonstandard" is not to imply that the dialect is incorrect or inferior. However, a nonstandard dialect does not have the support or sanction of governmental or educational institutions.
Dialects can be distinguished from: sociolects, which are varieties of a language spoken by a certain social class; standard languages, which are standardized for public performance (e.g.
A nonstandarddialect, like a standard dialect, has a complete vocabulary, grammar, and syntax, but is not the beneficiary of institutional support.
A dialect continuum is a network of dialects in which geographically adjacent dialects are mutually comprehensible, but with comprehensibility steadily decreasing as distance between the dialects increases.
Like any dialect, a nonstandarddialect has its own vocabulary and an internally consistent grammar and syntax; and it may be spoken using a variety of accents.
Describing a dialect as "nonstandard" is not to imply that the dialect is incorrect or inferior.
As a border-case, a nonstandarddialect 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.