Source : Free On-Line Dictionary of Computing

keyword
     
        1. One of a fixed set of symbols built into the syntax of a
        language.  Typical keywords would be if, then, else, print,
        goto, while, switch.  There are usually restrictions about
        reusing keywords as names for user-defined objects such as
        variables or procedures.  Languages vary as to what is
        provided as a keyword and what is a library routine, for
        example some languages provide keywords for input/output
        operations whereas in others these are library routines.
     
        2. A small set of words designed to convey the subject of a
        technical article.  Some publications specify a fixed set of
        keywords from which those for a particular article should be
        chosen.