Multi-firmness beds are queen or larger sized beds that are made with one firmness on one half of the bed, and another firmness on the other half of the bed. They are different from flippable beds, because the two firmness levels are on the same side of the mattress, and the bed isn’t designed to be flipped. Multi-firmness beds are very rare.
They are NOT technically split beds, since they’re all one piece. They are also NOT airbeds, since they can’t change firmness levels using a remote. They’re usually just hybrids, all-foam, or other mattress types that have one firmness on one half and another firmness on the other half.