The paper claim form used by physicians and other non-institutional providers; the 837P is its electronic equivalent.
Drug details live in box 24: the shaded upper portion carries the N4 qualifier, the 11-digit NDC, a unit qualifier and the quantity administered, while the unshaded lower portion carries the HCPCS code, modifiers, charge and units.
Most payers no longer accept paper, but the form's box numbering remains the common vocabulary for describing where data belongs on the electronic transaction.