It is a meditative absorption or trance, attained by a long practice of dhyāna. It is also a spiritual state of being totally aware of the present moment, a one-pointedness of mind.
In Sutra 1:17 Patanjali tells us that samprajnata samadhi comprises four stages: "Complete high consciousness (samprajnata samadhi) is that which is accompanied by vitarka (reasoning), vicara (reflection), sananda (ecstasy), and sasmita (a sense of 'I'-ness)." Sānanda is free from vitarka and vicara.
Ashtanga Yoga lists 4 samadhis : Ishvara-Samadhi(U.Path 16), Savikalpa-Samadhi(U.Path .17), Nirvikalpa-Samadhi(U.Path18) and Sahaj-Samadhi(U.Path19)
In Buddhism, samadhi is a state of concentration and also the last of the eight elements of the Noble Eightfold Path. It has here the meaning of 'concentration' which happens long before the above samadhis of Ashtanga yoga.
There are several forms of Samadhi :
- Sānanda samādhi - third level of the four samādhis of samprajnata samadhi as described in the Yoga Sutras 1:17
- Bhava samadhi - is experienced after the ishvara samadhi of Ashtanga Yoga
- Savikalpa samādhi - follows on the Bhava samadhi
- Nirvikalpa samadhi - the true enlightenment or Moksha without return
- Sahaja samadhi - an equivalent to parinirvana . Ramana Maharshi distinguished between kevala nirvikalpa samadhi and sahaja nirvikalpa samadhi. Mahasiddha Saraha - one of the founders of the tibetan Mahâmudrâ-Liage, saw Sahaja as the highest goal and as higher than Sunyata..
- Mahasamādhi, the act of leaving the body in the state of Samādhi