"Subject headings are not the same thing as keywords. Subject headings are standardized terms that are artificially created and added to a catalog record, in order to create points of commonality among topically related records that would otherwise be widely scattered by their many different keywords. The approved list of these terms is called Library of Congress Subject Headings (LCSH).
When you wish to search a library's catalog by subject, you have to come up with the correct headings appropriate to your topic. Often, the category terms used by the catalog are not the same as the keywords you might think of on your own. For example, books on "test tube babies" are not found under that phrase; the proper term is Fertilization in vitro, Human. Similarly, works on "moonshining" are cataloged under the heading Distilling, illicit. Searching the catalog by any keywords other than these exact headings will result in your missing most of the books on these topics."
To search the Library of Congress Subject Headings, enter your keyword into their search tool found below.