OEM - A company makes something for B company, designed by B company.
ODM - A company makes something for B company, designed by A company.
Bulk - Each packed in anti-static bag, several pieces put in a carton box with foams. Some have individual white/brown box.
For computer hardware, we call Bulk items OEM.
These are supposed to be sold to resellers/ system integrators (e.g. Dell, ABS) only, but Newegg (same company as ABS) sells them to end-users (you).
Some OEM hardware provide warranty to the end-users (you) - e.g. harddisk.
Some only provide warranty to the resellers/ system integrators, then they provide warranty to the end-users (you).
In the past, the price difference between OEM and retail was huge. But today the price difference is near nothing (e.g. retail cpu with 3 years warranty by Intel/AMD and OEM with 7-14 days warranty by the resellers). And you can find many hot deals that make retail products being cheaper than OEM. So it's not wise to buy OEM for most items now.