The traditional name (van 't Hoff) for a carbon atom that is attached to four different entities (atoms or groups), e.g. Cabcd.
See also: chirality centre
Sources:
Blue Book, p. 480 (https://www.acdlabs.com/iupac/nomenclature/)
PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2200 (https://doi.org/10.1351/pac199668122193)