My understanding of that is that you are calling for too many rpm that the eng cannot produce. At more rpm than the valve train can produce, valve springs not strong enough to close valves completely and rest of valve train trying to push the valves open, you have a condition of valves somewhere between open and closed, thus "floating". Not a good thing to do.
On hydraulic lifter cars, the valves will float quicker than solid lifter cars due to hydraulic action giving up quicker.
Easy to hear as when max rpm is reached, eng will start to stutter and miss.
Jim.