In theosophy, the monadic plane (hyperplane) or continuum/universe, enclosing and interpenetrating grosser hyperplanes, respectively is the plane in which the monad or holy spirit or oversoul is said to exist. The term is from the Greek word 'monad' and is used in the Arcane School ideas.
Theosophical differences
'Classical' 1800s Theosophy does not say the monad is human, but Annie Besant & Charles Leadbeater may have said so, and Alice Bailey or others, who uses similar ideas, did say so.
References
Monadic plane Wikipedia(Text) CC BY-SA