Cross reference:

A cross reference leads from an unauthorized heading to an authorized heading (see reference) or from one authorized heading to another (see also reference).  Actual cross references are generally not carried explicitly in authority records.  Instead, variant form and related headings are carried in authority records in either tracing or reference note fields.  Cross reference displays may be generated by combining the contents of a tracing or a reference note field and the 1XX heading field of a record.

Cross reference displays generated from the tracing fields are called simple cross references.

Cross reference displays generated from the reference note fields are complex cross references.