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.