Used in an established heading or established heading and subdivision record to trace a see from reference from a topical term not used in an established heading.

Subfield Codes
$a - Topical term entry element (NR). In UNBIS, the complete topical term is entered in $a.

Examples:

150   $a OFF ROAD VEHICLES
493   $a VEHICULES 4X4
493   $a VEHICULES DE LOISIR TOUS TERRAINS
993   $a VEHICULES TOUS TERRAINS

Tag 993 is «Heading-Topical Term (French)»