Subject headings are words and phrases which constitute a "controlled vocabulary" to categorize books by subject field. Subject headings often indicate the contents of books in terms that their titles (or your keywords) do not use, which often may be very general.
Use general subject headings for searching a broad topic or more specific subject headings for a specific author, historical period, or animal. You will find (more) headings specific to the subject category within the left-hand facets in our online catalog, Bobcat. If you want to see the subject headings for a specific title, click on the "details" link in the title record.