A word or phrase, or any combination of words, phrases, and modifiers used to describe the topic of a content object. Precoordination of terms for multiple and related concepts is a characteristic of subject headings that distinguishes them from controlled vocabulary terms. (ANSI/NISO Z39.19-2005)

National Information Standards Organization. (2005). Guidelines for the construction, format, and management of monolingual controlled vocabularies (ANSI/NISO Z39.19-2005). Bethesda, MD: NISO Press.