Deffinition of a floating slab
What are you building? Since you want an accurate definition the specific use and conditions permit similare slabs that are not exactly "floating", but are generally called floating.
A true "floating slab" example would be a garage slab the is poured between stem walls. It is not attached to the stem walls and is supported by the compacted soil beneath it.
The advantages are less of a tendancy to crack since the edges are not tied and the thickness and reinforcement can be less that a typical structural slab.
A basement floor is very similar, but not exactly the same. Much thicker slabs like slab foundations and post-teneioned slabs are also similar, since the soil supports the slab.