Authority control

From Ccslib.org

Authority control is a means of ensuring consistency in headings containing names, series, and subjects. This is achieved in part by storing the correct/authorized form of a heading in a separate MARC authority record; then catalogers can manually look up the authorized form and use that, and the system can link the heading in all bibliographic records in which it is used to the heading's authority record.

An authorized heading is found in the 1XX tag of a MARC authority record, an authorized See Also heading in the 5XX tag, and an unauthorized See heading in the 4XX tag.