Meaning of prescriptive grammar

prescrip'tive gram'mar

Pronunciation: [key]
  1. an approach to grammar that is concerned with establishing norms of correct and incorrect usage and formulating rules based on these norms to be followed by users of the language.
  2. a set of grammatical rules based on such an approach.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.