Good description:
RETAIL BOXED = you get the drive, software (bundle version, may be restricted/inferior options compared to retail of the same software), maybe one piece of sample media, maybe a decent printed manual, maybe a fitting kit of screws and audio cable.
OEM drives, you have to check, these are as supplied to system builders, brown boxed or just antistatic bagged, and do not neccessarily include any of the above unless actually stated.
If you want an OEM drive with software, make sure it says (or they confirm) that bundle software IS supplied with it.
There can be other differences - the OEM drives are sometimes named differently - particularly in the case of the SONY DVD writers, and use different firmware that may or may not have the same updates and capabilities.