company that makes a part or subsystem used in another company's product
OEM stands for Original Equipment Manufacturing. It is mainly used to describe parts for cars, airplanes and electrical systems. It is also used for computer parts and computer programs.
The name OEM is usually used when a new version of something is made by a company that is different to the company that first made it. The new company will sell the product at a cheaper price, but this is often because it does not have as many features as the first version. For example, an OEM computer program will usually only come with the disc and a licence, but no instruction manuals.