Apocrypha is one of the two new zones coming to ESO in the Necrom chapter. It is the Plane of Oblivion belonging to the Daedric Prince Hermaeus Mora, who will play an integral role in the Shadow over Morrowind storyline. 

Apocrypha is a repository containing untold amounts of knowledge, however it is a dangerous place for mortals and daedra alike - some of the secrets hidden here are closely guarded by Hermaeus Mora's servants, and are impossible to comprehend. Attempting to do so typically leads to madness.