Here is a confusing (and sometimes contradictory?) glossary of terms that are commonly used to describe parts sold by vendors or on eBay.
NOS part - NEW OLD STOCK part
This is a term used for an original, brand-new GM (Chevrolet or GMC truck) part that was never sold (usually this is a GM factory-manufactured or authorized part, sold by the dealer). This is the "gold standard" of parts. A NOS part is usually more valuable (especially if it is an original ACCESSORY part) if it is in a clean original box, with correct GM part number.
NORS part (two possible meanings)
(1) NEW OLD REPLACEMENT STOCK part
This is the term used for a brand new part that is direct replacement for an OEM or NOS GM (Chevrolet or GMC truck) part. This will usually be new suspension, electrical, lens or mechanical, etc. part made by outside suppliers to GM (Chevrolet or GMC truck), such as a bearing, brake part, electrical part, etc This will be brand new part that was never sold.
(2) NEW OLD REMANUFACTURED PART part
This is the term used for rebuilt or remanufactured part, either by GM (Chevrolet or GMC truck) or one of its outside suppliers, that was never sold. This type of part is usually associated with a steering, mechanical, or suspension part.
OEM part - ORIGINAL EQUIPMENT MANUFACTURER part
This is the term used for a part that was installed on the assembly line at the assembly plant. This part might have only been used at an assembly plant and was never offered by GM (Chevrolet or GMC truck) through their part system. Most NOS parts were made to replace an OEM part.
REPRO part – REPRODUCTION part
This is a term used for a part that is reproduced (by anyone, anywhere) for Chevrolet or GMC truck. Sometimes referred to as “Aftermarket Part”, this part is most often sold by vendors of restoration parts/products.
LICENSED REPRODUCTION part
This is a term used for a REPRODUCTION part that has been officially licensed by GM to be built (sometimes, but not always) to meet GM design and quality standards.
REPLACEMENT part
This is the term used for the part that was either made by GM (Chevrolet or GMC truck) or by some other outside supplier and it was designed to replace original OEM part. They may not look identical to the original part but they are designed to replace the original part.
FACTORY ACCESSORY (part)
This is a term used for a part that was listed by GM as an” accessory” part. The dealer sold this part and it could be installed either by the dealer or by the owner. Some examples are hub caps, mirrors, light/lamps, windshield washers, clock, radio, etc.
RPO – REGULAR PRODUCTION OPTION
This is a term used for an official GM option that was ordered by the customer/dealer and installed at the factory (this could be paint color combination, trim, or other part that was listed by GM as an option).
[Corrected typos and misspellings have been made, as pointed-out by Bill. Thanks, Tim]
