OEM stands for "original equipment manufacturer." This means that the rim was made specifically for your car by the same company that made the rest of the parts. Aftermarket rims are not made by the car's manufacturer but are made to fit your car. OEM rims are usually more expensive than aftermarket rims, but they are also higher quality. Aftermarket rims can be just as good as OEM rims, but they are often not as durable.