The Collaborative International Dictionary of English v.0.48:

nonstandard \nonstandard\, non-standard \non-standard\adj.
   1. varying from or not adhering to a standard; as,
      nonstandard windows; envelopes of nonstandard sizes;
      non-standard lengths of board cost more per foot. Opposite
      of standard. [Narrower terms: deficient, inferior,
      substandard]

   Syn: nonstandard.
        [WordNet 1.5]

   2. (Linguistics) Not conforming to the language usage of a
      prestige group within a community; as, a nonstandard
      dialect is one used by uneducated speakers or socially
      disfavored groups. Opposite of standard.
      [WordNet 1.5]