O.E.M stands for Original Equipment Manufacturer.
A more sound idea of what it's all about is that it's basic design or the standard of a product.
For instance. The Hercuels GeForce2 MX card, when purchased RETAIL, that is in the stores or in the box, comes with some nice 5.5ns SDram on the card. However, OEM Hercules MX cards usually have slower RAM.
It's a crazy world. Sometimes retail isn't as good as OEM, though it's usually the other way around. Sometimes there isn't much of or any difference at all. CPUs are a good example. ALthough there are those who will contest that the OEMs give you the lesser quality CPUs so you can't overclock as far. I don't know if this is true, but to be honost any OEM cpu I've gotten has yet to reach the AVG overclock listed on www.overclockers.com. THough my T-BIRD can, I just need a better cooling solution.
So, I hope that helps.
The Jolly Wizened Oaf!