HP 8200 Elite Intel Core i5 SFF Desktop

So what is an “external drive bay?”
Does that mean a box outside the box to hold a bare drive, or just an eSATA socket to plug in your own external drive/enclosure?

Gratias ago, caveat emptor, etc., and all that other good Latin stuff.

External bays are those that you can access/see from the outside of the case.

Internal bays are inside the case and can’t be seen when the case is closed.