Idamta is an important term in Mahayana Buddhism. The word idamt means ‘this-ness’ and denotes the absolute reality that is beyond all distinctions. This unique reality, which destroys all the notions of plurality and establishes the advaya (essence of being as one), will never be two or many. All that is seen as distinctive and as having an intrinsic nature is a mere reflection of that unique reality.
The monistic philosophy of Vijnanavada states that the unique reality is indescribable and anirvacaniya (indefinable), but it is variously characterized for common understanding as idamta (thisness), as idampratyayata (relation to thisness), as tathata (suchess), as the bhatatathata (suchness of existence), or as the most important term in the Vijnanavada doctrine, the “cosmic body of Buddha” (Dharmakaya).
In the philosophical position of the early Buddhists and the Vaibhasikas, nirvana is a stage that is beyond the phenomenal world (samsara); the extinction of samsara is the attainment of nirvana. These are considered as two realities somehow interconnected and linked together in a whole.
In the monistic conception of Vijnanavada, there is no real samsara or nirvana in definable terms, for these two are real only to one who is under the influence of the apparent world – ignorance.
The anirvacaniya (uncharacterizable) nature of the Absolute Reality is not totally unrealistic, or absurd like a city in the sky (Gandarvanagara) or vandhyaputra (the son of a woman who cannot conceive). It is something implicit in each phenomenal reality and can be experienced with prajna (wisdom) and upaya (right means). By combining these two aspects, one can achieve the bodhicitta (purified mind) and experience the idamta (thisness) of all phenomenal realities that reflects the advaya (oneness) beyond the apparent world. With certain characteristic differences, the conception of One reality is similar to the concept of Brahman in Advaita Vedanta.