What's the correct descriptive term for a toilet which has a base which rests on the floor but which discharges to the rear above floor level:
You have already described it. It is a "floor mount, rear outlet" toilet. As opposed to a floor mount, or wall mount toilet.
Next Q,: what is the correct name for the fitting to which it is attached, and for the gasketing method at the attachment (i.e.. the wall mount equivalent of "floor closet flange" and "wax sealing ring")?
Floor Mounted, Rear Outlet.
Normally you have a floor flange at the wall.
It takes closet bolts and either a foam rubber seal, or a reinforced wax seal that will say that it's good for wall mount printed on the box.