Glossary Definitions for difficult words and concepts are provided throughout the site. Definitions use pop-up windows (discussed later) to display pertinent information in a secondary window that can be kept open to use as a reference as the material is studied. Pop-up windows are accessed via hyperlinks (discussed later). There are also hyperlinks to an alphabetical listing of the entire Glossary. One such Glossary hyperlink is on the first page of each module and the other Glossary hyperlink is on the Sitemap page of each module.