OEM means Original Equipment Manufacturer. It is a term that refers to containment-based re-branding, namely where one company uses a component of another company within its product, or sells the product of another company under its own brand. OEM refers to the company that originally manufactured the product. In general, it is 100% fully functional software but lacks printed manuals, promo-discs and bulk-boxes. In some cases, it also lacks tech support from the manufacturer.

For a more detailed description of OEM see http://en.wikipedia.org/wiki/Original_equipment_manufacturer