Choosing the Visit Glossary menu item causes the
  current application glossary to be displayed in a
  separate Help window. A term can then be selected from
  the glossary, and its definition is displayed in the
  Glossary window.

  Note: Not all applications use the Glossary menu item.
  In these cases, the Visit Glossary menu item from the
  View menu and the Glossary... menu item from the Help
  menu are dimmed or missing.