Unestablished heading:

A heading that is not authorized for use in other MARC records as the lead element of a main, added, series, or subject access field. An unestablished heading may be a reference to a variant form of the established heading , a form of the heading used only for authority file organizational purposes, or a subject subdivision that is authorized for use with an established heading in an extended subject heading .

In authority records, unestablished headings are used in the 1XX (heading) and 4XX (tracing) fields of reference (008/09 , code b or c ), subdivision (code d ), reference and subdivision (code g ), and node label (code e ) records. An unestablished heading may also be used in the 4XX fields of established heading (code a or f ) records.