Glossary
Packing slip
A packing slip is the itemised note included in the parcel listing what was ordered. In print on demand it is normally white-labelled, carrying your shop's name and branding rather than the fulfilment provider's.
This is the one document every buyer sees, so it is worth treating as marketing rather than paperwork. A branded slip with a short note reads as a real business; an unbranded one that names a fulfilment company tells the buyer you did not make this.
Check whether your provider white-labels by default or only on request. It is the difference between a repeat customer and a buyer who now knows where to order direct.