Lorenzzo--Here (click on this link) is my best effort to explain "platform angle" (post #17 and subsequent, in the thread, "What is best edge angle for max grip?" from a couple years ago).
In short, "edge angle" refers to the angle of the ski base to the snow surface. Essentially, when combined with the ski's "sidecut radius," it determines the radius of the arc that the ski will bend into and carve on hard snow. Perhaps surprisingly, it has nothing to do with how well a ski holds.
"Platform angle" (and the related term, "critical edge angle," both terms coined by Ron LeMaster) refers to the angle between the ski edge (not necessarily the same as its base, due to base edge beveling) and the angle of the force applied to the ski by your body--what Zentune refers to as your "balance angle." Platform angle largely determines whether a ski grips or slips sideways.
The two are fundamentally different ways of measuring ski tipping, and they have completely different effects. Great skiing requires controlling both, constantly, and independently. Please read the thread I linked to above for (much) more. And feel free to paste text and/or images from that thread here if you want more discussion.
That thread is a terrific read relative to these concepts. Big time thanks for the reference. I suspect I need to progress past Chapter 2 to ask meaningful questions as successive chapters address turn anatomy, technique and real world conditions.
The animation showing progression of edge angle, etc. is interesting and insightful relative to how edge angle changes through the turn and as steepness changes.