We've developed a glossary in the Resources section of our site to help you to learn more about dark matter. You can also check in the Resources section under People In the Book for authors who have written on dark matter and links to their works and other great thinkers involved with dark matter. On the menu above select Resources and then Glossary. From there you will have an alphabetical listing. Simply choose "D" for dark matter and you will find definitions for this term and many others.