OEM

OEM stands for Original Equipment Manufacturer, and denotes a software or hardware unit that is unavailable through standard retail channels (although it's not uncommon to see OEM equipment being sold at retail, they often lack parts that the full retail products do, since they were never intended to be sold separately).

Original Equipment Manufacturer is actually a misleading term; OEMs buy computers in bulk and customize them for a particular application or demographic. They then sell the customized equipment under their own name. The term is really a misnomer because OEMs are not the original manufacturers - they are customers of the original manufacturers.