A character-string of not more than 31 characters that forms one of the
  following:

  function-name
    A COBOL word that names a mechanism provided to determine
    the value of a function.
  reserved word
    A COBOL word specified in the list of words that can appear in a
    COBOL program.  A reserved word cannot appear in a program as a
    user-defined word or system-name.
  system-name
    A COBOL word that has already been defined by the implementor to
    refer to the program's operating environment.
  text-word
    A character (or a sequence of characters) in a COBOL library, source
    program, pseudo-text, or dictionary that is subject to certain
    restrictions.
  user-defined word
    A COBOL word that must appear in the source program to satisfy the
    format of a clause or statement.
  verb
    A word that causes the compiler or object program to take action.