Keyword and subject searches are not the same thing, but both are part of an effective strategy for searching databases:
Subject headings provide a standard vocabulary for describing the content of materials. The UNC-Chapel Hill Library Catalog uses the Library of Congress (LC) Subject Classification System. Other databases may use different subject systems. Unlike keywords, the terms that you use in a subject search must match the exact format of the subject headings.
Here are some examples of Library of Congress subject headings in Physics: