OEM products (not just motherboards) are intended for bulk purchase by another company who either sells them as their own products or use them as components for assembling their own products.
The basic design is usually the same as a boxed retail product, but may come without certain accessories such as connectors, screws, etc. They may also differ in some details, labeling and finishing. The packing is usually different too and may be nothing more than a plastic wrapper or plain carton.
It is possible that an OEM product may not have been tested as carefully as a retail item at the factory.
They may also have different warranty terms. Be sure to ask about that before buying an OEM item.
I'm not sure about the price, but it seems to me that you could also buy box packed versions for that price, maybe for a little less in a major city.
