Library of Congress Subject Headings (LCSH) is a list of words and phrases – called headings – that are used to indicate the topics of library resources. It is used by most academic and research libraries in the United States, as well as by many public and school libraries. It is also used by libraries throughout the world.
LCSH brings consistency to library collections by categorizing topics into logical arrangements, and by controlling synonyms, variant spellings, and homographs. For example, one author may use the phrase "soda pop", another may say "soft drink"; yet another, "soda"; and a fourth, something else, but they all intend to refer to the same type of beverage.
In LCSH, one of those words or phrases is used as the heading, and the others refer to it. By using only one word or phrase for each topic, librarians can make sure that all of the resources on a topic will be grouped together, thereby allowing users to find them easily.
From “Process for Adding and Revising Library of Congress Subject Headings” https://www.loc.gov/aba/cataloging/subject/lcsh-process.html
Subject Headings are terms that are most commonly used to describe the topic that a resource covers. Unlike keywords, which are user generated, subject headings are created and maintained by an authoritative institution. Since Williams Libraries organizes our resources using the Library of Congress Classification, we also utilize Library of Congress Subject Headings to provide access to our collections by subject.
Subject headings are arranged systematically, and can be useful tools to help browse the collection by topic. Subject headings for each resource are located in the "Details" section of the catalog record, under "Subjects."