CPO: Acronym for "Control Panel Overlay." A CPO is a piece of vinyl or similar material originally used to cover the metal or wood control panel, display control instructions and branded game art.
NOS: Acronym for "New Old-Stock." This term is most commonly used to describe original, unused vintage items for sale or auction. Many times unused stock may be found stored away untouched for years. NOS items are not reproductions, they were manufactured by the original manufacturer and should be close to perfect condition.
OEM: Acronym for "Original Equipment Manufacturer." An OEM was the originator of a specific part. Parts from an OEM should be more accurate than reproduction parts made for the aftermarket. Reproduction parts are usually not considered 100% fully interchangeable with parts from the OEM.