One of nine Realms in the Deep Umbra said to have been a part of Gaia in ages past. Each corresponds to a Sphere of magick & is said to be ruled by a Celestine.
Shade Realms are doors to Shard Realms (but not the only way to get there).
Infinite Tapestry states: each of the 9 planets holds a Shard Realm. Before the Avatar Storm, the Shade Realms were reflections cast on the First Horizon. Shade Realm/Shard Realm of Life (Venus) in Infinite Tapestry pg. 121 is interesting. Dangerous wildlife gone wild.