The term NOS comes from the words new+old+stock. These are parts or accessories that were manufactured in the past (old) that were never used and are being sold now as new.
There are OEM ( original equipment manufacturer) inventories as well as aftermarket replacement inventories. Purists in restoration projects only consider OEM parts to be NOS. This is mostly semantics as long as a product is being sold under the proper brand.
Unazom sells NOS parts from many manufacturers, both OEM and aftermarket. Ours products are named properly.