The Library of Congress Subject Headings (5 vols.) provides an alphabetical list of of the "correct" subject headings used in the Library Catalog.
It will also direct you from commonly used "incorrect" terms to the "correct" term.
For instance if you look up "photos", the guide will refer you to the correct term - "photographs ".
It will also provide broader, narrower, and related terms - and, in many cases, the Library of Congress Call Number.
Public Worship - BF5-BV26
Worship - (Broader term)
Drama in public worship - (Narrower term)
Church attendance - (Related term)
Unlike the Internet, the Library Catalog and most databases use what is called a "controlled vocabulary" to place all variations of a topic under an official subject term. Examples:
You wouldn't want to type five different search terms just to research one topic - soda or pop or soda pop or cola or carbonated drinks or soft drinks? If you knew the official subject term - soft drinks - you would only have to type the one term.
Subject searches (used in the advanced search mode) narrow your search by searching only the Subject field. Key Word searches examine the Author, Title, Subject, and Note fields...and may provide unintended results.
For instance, a Key Word Search for Art might find:
But a Subject Search for Art would only find materials on that topic.