Controlled vocabulary--also known as subject headings, subject terms, thesaurus terms, or descriptors--are the official indexing terms used by the organizers of a
database to describe each concept so that all items on the same topic have the
same descriptor or subject heading.
contrast to “free Web” searching, controlled vocabulariesorganize the
information in a database. You can click on a heading to see all the other items that have the same heading. You can also combine the terms in a new search to find items on that topic.
Your search results will be more focused and more relevant, since you will be searching directly in the subject or descriptor