bonding number

The bonding number n of a skeletal atom is the sum of the total number of bonding equivalents (valence bonds) of that skeletal atom to adjacent skeletal atoms in a parent hydride, if any, and the number of attached hydrogen atoms, if any. Examples: SH2: for S, n = 2; SH6: for S, n = 6.
Blue Book (Guide), p. 21
See also:
PAC, 1984, 56, 769 (Treatment of variable valence in organic nomenclature (lambda convention) (Recommendations 1983)) on page 774