1.Definition: not conforming to the language usage of a prestige group within a community

"A nonstandard dialect is one used by uneducated speakers or socially disfavored groups", "The common core of nonstandard words and phrases in folk speech"

2.Definition: not standard; not accepted as a model of excellence

"A nonstandard text"

3.Definition: varying from or not adhering to a standard

"Nonstandard windows", "Envelopes of nonstandard sizes", "Nonstandard lengths of board"