Can someone please explain to me what "Hermaeus Mora's Apocrypha" is, and why UESP suggests that it is hinted in the trailer? (knows nothing about it - but very interested in reading some text-walls should they be provided to me)

mora is a daedric prince
apocrypha is his plane of oblivion
like the deadlands are dagons plane
its just the name of the realm that he controls