The complete alphabetic list of controlled vocabulary created by catalogers and used in cataloging since 1898 at the Library of Congress in assigning subject headings to facilitate accessto the information content of newly published works. The list has syndetic structure in the form of USE references to direct the user from a synonym or quasi-synonym to the preferred term, and UF (used for), BT (broader term), RT (related term), and NT (narrower term) notes to indicate semantic relations between headings. Reference librarians often refer to the list as "the big red books" because it is published annually in several large volumes traditionally bound in red.