A nonstandard dialect is a dialect that does not have the institutional support or sanction that a standardized dialect has.
Like any dialect, a nonstandard dialect 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. Also prestige dialects 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, the term eye dialect may be used for nonstandard phonemic spelling.
It is uncommon in written texts unless the text is dialect poetry, etc.
Famous quotes containing the word dialect:
“The eyes of men converse as much as their tongues, with the advantage that the ocular dialect needs no dictionary, but is understood all the world over.”
—Ralph Waldo Emerson (1803–1882)