Subject headings are official terms used to precisely describe the content of documents and publications. Librarians, indexers, or sometimes the authors themselves assign the terms by reviewing the content of the item and selecting appropriate terms from an official, standardized list. This list of subject headings is generally called a thesaurus. Because subject headings can be selected only from a standardized or "controlled" list, searching a database by using official subject headings is also known as controlled vocabulary searching.
When you do a subject search in a database, your search looks through the database at all of the entries in the "Subjects" and pulls out any records that exactly match what you typed.
The following book would only be retrieved in a subject search if you typed one of the three subject headings exactly:
