A word that has a specific role in the context in which it occurs, and therefore cannot be used for other purposes. For example, in many programming languages the words ‘IF’ ‘THEN’ ‘ELSE’ are used to organize the presentation of the written form of statements (between ‘THEN’ and ‘ELSE’ and following ‘ELSE’) whose execution is governed by the value of the Boolean expression between ‘IF’ and ‘THEN’. The use of if, then, else as identifiers is thus not permitted in these languages since they are reserved words. See also keyword.