From www.leather-dictionary.com - The Leather Dictionary
Flesh side or flesh split is the back of top grain leather which was connected to the meat. The grained top side is also called "hair side".
The flesh side is the side which is separated from the meat.
If the flesh side is processed to the outside, this surface is called suede.
Typical sheepskin jacket - inside fur and outside flesh side = suede.
Video about split leather and PU leather
Video about the production of split leather and PU leather