The word yoga’ means to yoke or unite and is used to imply the means or path by which the individual soul unites with God. It is not to be confused with physical exercises alone Yoga has eight types of disciplines.
The first two, Yama and Niyama, purify the heart and bring about ethical discipline. Yama means abstention from evils of all types; killing, untruth, property, etc. Niyama means observance of purity and practice of austerities.
The next three steps, Asana, Pranayama and Praryahara are preliminary to Yoga. Asanas are yogic postures which, when practiced steady the mind for concentration and discipline the body. Pranayama are breathing exercises which improve the condition of the lungs, the heart and the nervous system. Pratyahara means shutting out all outward impressions from the mind and looking inward.
The last three steps are called Raja Yoga and include Dharana, Dhyana and Samacihi. Dharana means concentration on any one subject which could be a light within one’s mind. Dhyana or meditation involves an unceasing flow of thoughts and ideas toward this object. Such meditation leads to the final state known as Samadhi, when the subject of the meditation and the object becomes one.
Samadhi itself has two steps. In the first, the conscious samadhi, the yogi attains supernatural powers by the strength of his yogic practices becomes clairvoyant adept at at mind-reading and thought-transmission. The yogi, who ignores such powers and progresses further, attains the superconscious or nirvikalpa samadhi. The yogi in this stage is a liberated soul.
Samadhi is still practiced by some sadhus (holy men), specially in the Himalayas where they live in caves. It is said that they have the ability to slow down their heartbeats. They lie down in a box which is buried 10 to 12 feet underground where they remain for many days.