What is a bare or OEM hard drive?

Does they have the connector chip on them. Because everywhere I see image of bare drive as showing the spindle and platter.

Yes, they are fully functional hard drives. What you are describing when you say you see an “…image of bare drive as showing the spindle and platter…” is most likely a marketing photo attached to a listing on a website to show you something. Because let’s face it: Hard drives are boring tiny boxes that don’t photograph well. Otherwise, the drive is fully functional & has the proper connectors; it just won’t have the cables, CDs, manuals and other junk that comes with a “normal” non-OEM drive.

There's little practical difference between a 'retail' or 'OEM' HDD for consumer systems. For the same model, its the exact same disk drive, with all the relevant internal parts needed to make it function. In general such drives are primarily marketed at system builders (who'd rather get a padded box of drives with just the necessary packaging).

In general OEM packaging looks like this

You have a drive in a sealed bag, and that's it. No SATA cables, manuals or anything else.

Drives absolutely do not ship with exposed platters

Depending on the type of drive and the SKU you may get some additional literature (like manuals), a sata cable, or in the case of some SSDs a 'migration kit' that would let you hook up your drive over USB, image, and swap drives.

I'd also add if it is a prebuilt PC, or server in some cases the replacing the 'OEM' drives that come standard with it have your own drives (OEM or otherwise) may void the warranty. Some may also have specific firmware versions or be branded to the system builder.