Comment by jsheard
I disagree with Wikipedia's definition covering any design where the guts are visible from either side, in my experience "skeleton" always refers specifically to the dial being hollowed out or transparent. When the dial is opaque but the rear is transparent it's usually called an "exhibition caseback" instead.
Agreed, and also most skeleton watches have the actual movement routed out to remove much of the material from bridges and plates, to expose as much gearing as possible.