Original Equipment Manufacturer ,eg. Dell,H.P.Buy these from people like maxtor in mass quantities. it basically means that there are not extra goodies such as software and owner's manuals with the hardware you purchased and a shorter warrantee.
Just look at the label on the Drive .There should be information on who made it and a model # then you can go to their site if you need any software.But you should see it's configuration numbers on the faceplate tabs to enter into the bios manually if the bios does not auto configure it.
However, do you not see an area on the smallest side with little brass pins sticking out?
If you do not I do not know what you bought , but it is not a complete ide internal Harddrive.