What is Samadhi

Samadhi is a state of mind, when the consciousness about him/her is lost and only objects remain. Steadiness and tranquillity of mind is essential for Samadhi which is achieved by observing eight limbs of self-discipline.
 
There is a difference between Sleep and Samadhi. In Samadhi manas (मन) is retired from the attachment of all sensual pleasures and is fully restrained. In sleep, manas is oblivious of the world but is not fully unattached to sensual pleasures. Sleep is tamsika. In Samadhi, manas is fully unattached to sensual pleasures.
 
Limbs of Self-Discipline:
The great Patanjali rishi prescribed eight limbs for self-discipline of Yoga to eliminate distractions of mind called as chitvritti viz. Yama (Self-restraints), Niyama (observances of rules), Asana (postures), Pranayama (regulation breath), Pratyhara (abstraction), Dharna (concentration), Dhyana (meditation), Samadhi (trance). (A separate detailed article on Patanjali yoga darshan is already published under the category of Philosophy)
 
Samadhi with open eyes:
Dispassion and steadiness of mind need to be achieved, while performing the worldly actions. In case, the mind is unsteady when the eyes are open, it is insentient Samadhi. Rishi Vishwamitra remained in Samadhi for sixty thousand years but when he opened the eyes, he fell in glamour of Menka.
 
Gopis used to go in state of Samadhi with open eyes. When Udhav ji explained the concept of Nirgun & Nirakar Brahman to Gopis and the need to meditate on it, Gopis said to Udhav ji that they see Shri Krishna everywhere and meditate him with open eyes. What is the need to meditate on Nirakar Brahman?  
 
Types of Samadhi:
Samadhi is of two types’ viz. Samprajaatah Samadhi and Asamprajaatah Samadhi.
Samprajaatah or seed Samadhi: When distractions/modifications of mind are fully destroyed, this state is called Samprajaatah Samadhi or Samadhi with consciousness. Samprajaatah Samadhi is of four type’s viz. Savitarka Samadhi, Nirvitarka Samadhi, Savichar Samadhi and Nirvichar Samadhi.

1. Savitarka Samadhi is that in which knowledge based only on words, wisdom and ordinary knowledge based on sense perception or reasoning are present in a mixed state and the mind alternates between them. This is first state.
2. Nirvitarka Samadhi is attained when mind becomes clear and loses its essence. In this state the mind loses the ordinary knowledge based on perception or reasoning and words. This is better state.
3. Savichar Samadhi is attained when Brahman is not witnessed but wisdom is attained.
4. Nirvichar Samadhi is the Samadhi in which satchitananda Brahman is witnessed (dawn of spiritual light).

Asamprajaatah or seedless Samadhi: On attaining excellence in Nirvichar Samadhi, one becomes pure and witness Brahman and becomes above pains of death. In this stage, all desires, ignorance, afflictions, sufferings, impressions etc. retire. As per Mandukya Upanishad (2.2.3), such wise person attains moksha.