The term “spa” is often used to describe an in-ground spa. An in-ground spa is a body of water built into the ground, much like an in-ground pool.
The term “hot tub” is typically used to refer to an above-ground portable spa. A hot tub or portable spa is a completely self-contained vessel. All of the plumbing, as well as the electrical control system and other components, are built inside the hot tub cabinet.