For each subject, the most precise term naming the subject, rather than a broader or generic term which encompasses the subject. In rare cases, a broader term may be used when the most specific term is deemed too narrow and therefore not likely to be sought by catalog users. Furthermore, each subject heading is listed directly under its most specific name, rather than under a broader or generic term that encompasses it.

See also:

3.0 Fundamental principles of Library of Congress Subject Headings