Samadhi is the eighth and the final step of the Ashtanga Yoga of Patanjali. This is the last stage of the concentration of the mind. This is the climax of the mental manipulation during the practice of Yoga. 

Patanjali describes that state as Samadhi when there is consciousness only of the object of meditation and not of the mind itself. 

When the state of Dhyana has been well established and the mind is able to hold the object of meditation without any distraction, it is possible to know the object much more clearly than in ordinary thinking.

The Dhyana precipitates into Samadhi with the complete disappearance of the self-awareness.

The apparent disappearance of the self-awareness means dissolution of subject-object relationship and their fusion in consciousness. 

With the disappearance of the self-awareness of the mind, a higher consciousness starts operating and the perception of the ultimate reality i.e. the reality hidden behind the object takes place. 

Here the perceiver, the object of perception and the perception fuse into one phase. 

Thus Samadhi is only an advanced state of Dhyana, the only difference being the elimination of the self-awareness of the mind during Samadhi.  

The essential feature of the Samadhi is the disappearance of self-awareness leading into the realisation of Ultimate Truth which may be associated with unresponsiveness of the body.

The unresponsiveness of the body alone without the transformation of the consciousness is some times known as Jada Samadhi. This is not a true Samadhi .

The person coming out of the Jada Samadhi will not have any mental achievement while a person coming out of a true Samadhi brings with him the transcendental knowledge, wisdom, peace and strength of the inner life. 

Samadhi is the stage when there is consciousness only of the object of meditation and not of the mind itself.

Samadhi, as described in the texts is the means to attain Nirvana. However, in today's world we can understand Samadhi in more practical terms.

One can become oblivious of the things around him if he is detached from them.

Thus in the state of Samadhi, one just performs his functions without caring for the results that his deeds will yield.

The positive results do not make the person happy and the negative ones do not make him sad.

It is in this stage of Samadhi that one can look deep within himself for self-awareness. Thus, in other words, Samadhi is self-awareness.

In the stage of Samadhi, one is completely detached from the materialistic worldly emotions and this gives him the opportunity for self-analysis.