Dharmadhatu

Dharmadhatu (Sanskrit) is the 'dimension', 'realm' or 'sphere' (dhātu) of the Dharma or Absolute Reality.
Definition.
In Mahayana Buddhism, dharmadhātu (; ) means "realm of phenomena", "realm of truth", and of the noumenon. It is referred to by several analogous terms from Mahayana Buddhist philosophy, such as Tathata (Reality "as-it-is"), emptiness, dependent co-arising and eternal Buddha. It is the "deepest nature, or essence".
Dharmadhātu is the purified mind in its natural state, free of obscurations. It is the essence-quality or nature of mind, the fundamental ground of consciousness of the trikaya, which is accessed via the mindstream.
When the buddha-nature has been realised, dharmadhātu is also referred to as the Dharmakāya, the "Body of Dharma Truth".
It is associated with Vairocana.
Historical origin.
Kang-nam Oh traces the origin of dharmadhatu to the Avatamsaka Sutra. It has been further developed by the Hua-yen school:
Understanding in Buddhist tradition.
Indian Buddhism.
Śrīmālādevī Sūtra.
The Śrīmālādevī Sūtra (3rd century CE), also named "The Lion's Roar of Queen Srimala", centers on the teaching of the tathagatagarbha as "ultimate soteriological principle". It states that the tathagata-garbha is the "embryo" of the Dharmadhatu and the Dharmakaya:
In the Śrīmālādevī Sūtra, there are two possible states for the Tathagatagarbha:
The sutra itself states it this way:
"Dharmadhātustava".
The "Dharmadhātustava" ("In praise of the Dharmadhatu"), attributed to Nāgārjuna though questioned, is a treatise on the dharmadhatu. According to the "Dharmadhātustava", the dharmadhatu is the ground which makes liberation possible:
According to the "Dharmadhātustava", the dharmadhatu is seen when the afflictions are purified:
Chinese Buddhism.
Mahaparinirvana Sutra.
In the Mahayana Mahaparinirvana Sutra, the Buddha states of himself that he is the "boundless Dharmadhatu" - the totality itself.
Tibetan Buddhism.
Five Wisdoms.
The Dharmadhatu is comprehended by one of the Five Wisdoms:
Dzogchen.
In the Dzogchen text "Gold refined from ore" the term Dharmadhatu is translated as 'total field of events and meanings' or "field of all events and meanings".