oem = original equipment manufacturer, i.e., Ford Motor Company. NOS = new old stock or new order stock. Those are parts that Ford (or the car part maker) built for a certain vehicle as a replacement for the oem part. The NOS part was never sold to anyone, so some third party company bought that stock from Ford. National Parts Depot is an example of a company that sells NOS parts. They also bought some of the dies or tools to make the oem parts, and make oer parts, sometimes called "re-pops". Reproduction parts might be made onthe original tooling, or are a close copy. LMC Truck is an example of a company that sells some re-pop parts as well as oem. THe NOS parts are usually more expensive than re-pops, and what you want to use for a show-guality restoration. For a daily driver or otherwise regular vehicle, re-pops are much cheaper, do about the same thing as the oem part, and usually fit close enough to work with. AN example is my Shaker scoop and intake, which is a $400 repop from a company in Australia. A NOS 1970 Mustang Shaker assembly goes for about $1800-$2000. JSM84