The Library of Congress Genre/Form Terms for Library and Archival Materials (LCGFT) is a thesaurus that describes what a work is versus what it is about. For instance, the subject heading Horror films, with appropriate subdivisions, would be assigned to a book about horror films. A cataloger assigning headings to the movie The Texas Chainsaw Massacre would also use Horror films, but it would be a genre/form term since the movie is a horror film, not a movie about horror films.

The thesaurus combines both genres and forms. Form is defined as a characteristic of works with a particular format and/or purpose. A "short" is a particular form, for example, as is "animation." Genre refers to categories of works that are characterized by similar plots, themes, settings, situations, and characters. Examples of genres are westerns and thrillers. In the term Horror films "horror" is the genre and "films" is the form.

LCGFT assumed its title in June 2010 and in May 2011 the LCCN prefix "gf" was implemented to identify Genre/form terms as part of the change to separate LCGFT from LCSH. The "gf" prefix is one way by which a record can be identified as a genre/form authority record. Further information about the LCGFT thesaurus and its relationship to the LCSH data set may be found in Library of Congress to Reissue Genre/Form Authority Records (Revised May 9, 2011) and in a FAQ on the topic.