The Hover Charm is a spell which makes the target hover in mid-air for a brief period of time. It was used by Dobby the House-Elf in 1992, though Harry Potter was blamed for it.
Behind the scenes
Although this spell and Wingardium Leviosa are seemingly the same spell, they are not. The Hover Charm makes the target hover, statically, whereas Wingardium Leviosa makes objects fly, the caster having some degree of control of where they fly to.
On Pottermore, the cake only hovers for fourteen seconds before smashing; such may indicate that the spell has a time limit. However, it is more likely that Dobby only waited fourteen seconds before dropping the cake.
This spell and Levioso have curiously similar effects; it may be that the two are the same, or potential variants.