Source : Webster's Revised Unabridged Dictionary (1913)

Grammar \Gram"mar\, n. [OE. gramere, OF. gramaire, F. grammaire
   Prob. fr. L. gramatica Gr ?, fem. of ? skilled in grammar,
   fr. ? letter. See {Gramme}, {Graphic}, and cf. {Grammatical},
   {Gramarye}.]
   1. The science which treats of the principles of language;
      the study of forms of speech, and their relations to one
      another; the art concerned with the right use aud
      application of the rules of a language, in speaking or
      writing.

   Note: The whole fabric of grammar rests upon the classifying
         of words according to their function in the sentence.
         --Bain.

   2. The art of speaking or writing with correctness or
      according to established usage; speech considered with
      regard to the rules of a grammar.

            The original bad grammar and bad spelling.
                                                  --Macaulay.

   3. A treatise on the principles of language; a book
      containing the principles and rules for correctness in
      speaking or writing.

   4. treatise on the elements or principles of any science; as,
      a grammar of geography.

   {Comparative grammar}, the science which determines the
      relations of kindred languages by examining and comparing
      their grammatical forms.

   {Grammar school}.
      (a) A school, usually endowed, in which Latin and Greek
          grammar are taught, as also other studies preparatory
          to colleges or universities; as, the famous Rugby
          Grammar School. This use of the word is more common in
          England than in the United States.

                When any town shall increase to the number of a
                hundred families or householders, they shall set
                up a grammar school, the master thereof being
                able to instruct youth so far as they may be
                fitted for the University.        --Mass.
                                                  Records
                                                  (1647).
      (b) In the American system of graded common schools an
          intermediate grade between the primary school and the
          high school, in which the principles of English
          grammar are taught.

Grammar \Gram"mar\, v. i.
   To discourse according to the rules of grammar; to use
   grammar. [Obs.] --Beau. & Fl.

Source : WordNet®

grammar
     n : studies of the formation of basic linguistic units

Source : Free On-Line Dictionary of Computing

grammar
     
        A formal definition of the syntactic structure of a language
        (see {syntax}), normally given in terms of {production rule}s
        which specify the order of constituents and their
        sub-constituents in a {sentence} (a well-formed string in the
        language).  Each rule has a left-hand side symbol naming a
        syntactic category (e.g. "noun-phrase" for a {natural
        language} grammar) and a right-hand side which is a sequence
        of zero or more symbols.  Each symbol may be either a
        {terminal symbol} or a non-terminal symbol.  A terminal symbol
        corresponds to one "{lexeme}" - a part of the sentence with
        no internal syntactic structure (e.g. an identifier or an
        operator in a computer language).  A non-terminal symbol is
        the left-hand side of some rule.
     
        One rule is normally designated as the top-level rule which
        gives the structure for a whole sentence.
     
        A grammar can be used either to parse a sentence (see
        {parser}) or to generate one.  Parsing assigns a terminal
        syntactic category to each input token and a non-terminal
        category to each appropriate group of tokens, up to the level
        of the whole sentence.  Parsing is usually preceded by
        {lexical analysis}.  Generation starts from the top-level rule
        and chooses one alternative production wherever there is a
        choice.
     
        See also {BNF}, {yacc}, {attribute grammar}, {grammar
        analysis}.