Architects and engineers (both are building professionals) call them footings.
Footings are part of the load path from the roof, so their purpose is to help bear the load that other parts of the slab typically don’t experience. They extend below local frost lines so that soil heaving from expansion as it freezes doesn’t damage the slab.
Drilled pier foundations are used where expansive soils are a problem and they usually have voids beneath the slab perimeter except where the piers are located. I’m not so sure they use them with slab foundations. I’ve only seen them used with crawlspaces and basements.
Monolithic slab