A drop-in tub is essentially a shell with feet and a rim.
You can install a drop-in tub in the bathroom or in an alcove. It is then lowered into a bespoke raised platform deck, which not only conceals the plumbing and the uncovered sides of the tub but also provides a seating area for when you are entering and exiting the tub.
The bathtub, on the other hand, is not supported by the platform.