Oh God, please let`s not open that Pandora`s box again...
Okay, in essence a the falling leaf is zig-zagging across the hill without making an edge change. You simply ride across the slop, turning uphill to slow to a stop, then you start sliding the other way and so forth.
While not prohibiting it being taught, AASI has discouraged the overuse of the riding task because too many instructors would teach falling leaf and leave it at that. Now we have thousands of sideslippers, heel edging their way around the mountains..
The best way to control speed is to make lots of short radius turns and skid the tail to bleed off momentum.