For non-dualists, samādhi has the meaning of absorption in self-knowledge 'aham brahmasmi', I am brahman.

But the common meaning of samādhi is nirvikalpa samādhi. There are no more representations of objects in the mind, no more various concepts (vikalpas), no more mental movements (vṛtti's), but there is the full experience of the presence of existence and consciousness.

Note: There are no (nir) mental objects or divisions (vikalpas) in nirvikalpa samādhi. Just as in deep sleep, the objectless is experienced. But the difference with deep sleep is that instead of the absence of objects, the presence of existence-being is consciously experienced. This is a very subtle vṛtti, because it is an experience of the unmanifested (avyakta), and therefore an experience.

Brahman as such can never be experienced. Because it is what makes experience possible. This is the first reason why nirvikalpa samādhi is not a mokṣa.

In this type of samādhi, therefore, the mind is perfectly equal (sama) to cognition (dhi), as a completely empty mirror, reflecting medium. But it is still a state of mind. And the mind is simply not the self (reason number two).

In nirvikalpa samādhi there is no experience of distinction between knower-knowledge-known, just as in deep sleep. But: Unlike sleep, the mind is awake, which means that vṛttis are possible, and therefore the state will lead to thinking again. That is the third reason why this state is not freedom (mokṣa). Samādhi takes place in time and will therefore end.

Because the mind is changeable, every samādhi is impermanent and cannot be an experience of ātma, because ātmā cannot be experienced. Think about it: Waking and dream states and nirvikalpa samādhi express a duality (reason number four) because they alternate in the same realm of unmanifested and manifested.

Therefore, nirvikalpa samādhi is reflected bliss, which is mithyā, because it is borrowed and dependent on the original ānanda of consciousness (reason number five). Attributing authenticity to reflected bliss is ignorance, and therefore it is also considered a subtle vṛtti. A person who regularly experiences nirvikalpa samādhis will become attached to them.

Because you can come into samādhi, it is something that is attained. Whereas mokṣa is the freedom that is alone, and 'always' was. Although sleeping is technically something else, the subsequent duality between waking and sleeping is the same as the duality between samādhi or not.

Some say that the world looks very different after nirvikalpa samādhi, but that is not true, because how I see the world depends purely on my knowledge of reality. After you have experienced nirvikalpa samādhi, you have to interpret that experience. And to interpret the experience you have to have a pramāṇam, a means of knowledge. So, all in all, nirvikalpa samādhi is not a mokṣa. Mokṣa is the freedom to be free consciousness forever.

In deep sleep (suṣupti), thoughts are unmanifested. In nirvikalpa samādhi, thoughts are also potentially ready on standby, and will reappear after the immersion. The pull of prārabdha karma (karma working out in this life) brings the person out of nirvikalpa samādhi (or out of suṣupti, deep sleep), and again projects the world. There will be potential, individual ignorance (ajñāna vṛtti), ready to manifest itself as the old song of a story in a world.

In yoga (aṣṭāṅga yoga), written down in eight steps by patañjali in the yoga sūtras, nirvikalpa samādhi is the final goal. It is a system to train you to equality of mind. Yet it will never be permanent. People may not sufficiently see that what they are trying to achieve, non-dual consciousness, is already the case. Every experience, every object, is already nothing but a (temporary) manifested expression of the self.

Aṣṭāṅga yoga is of course very useful to prepare you for freedom. The pitfall, however, is that the meditator or yogi is so attached to or proud of his samādhis that she or he will not recognize the value of self-knowledge. Conversely, it is quite possible that the jñānī practices samādhis for fun, she also knows that he is not the doer. But this is not logical, because the jñānī is always full and satisfied as it is, and will therefore not easily experience an incentive to feel different from what īśvara tells her or him.

Thus we come to savikalpa samādhi: Equality of mind with (sa) vikalpas, seemingly diverse thoughts and forms of the world in the mind. This is the apparent state of the wise. Her or his mind sees everything with open eyes as waves in the same (samā) ocean of consciousness. This seeing is therefore done with the eye of knowledge (also called the third eye). According to the truth, this free sage is consciousness, and sees everything as the same, because she or he knows! The experience is then a fullness, contentment, unity. Even though thoughts apparently occur, and a world appears. It's like meditating or contemplating with your eyes open. But pure savikalpa samādhi cannot be meditation or contemplation. To see everything equally in the mind, even knowledge (jñāna-yoga) can no longer be practiced. The sage is then simply the whole existence, regardless of what keeps appearing.

This is sophisticated business. Both the knower in the mind and the purest reflection of truth in the mind (akhaṇḍa ākāra vṛtti) are experienced as not real. In pure savikalpa samādhi, one is singular what one is (brahman, consciousness, aloneness), regardless of what happens, and including "everything." So the sage knows that the whole concept of savikalpa samādhi with the appearances of that mithyā is false (dependent, changeable and impermanent).

Nirvikalpa samādhi is also called asamprajñāta samādhi or nirbīja samādhi.