The word Dhyana has been derived from the Sanskrit word 'Dhi', which means to contemplate, reflect, think or be occupied in thought. According to Maharishi Patanjali:
"An incessant flow of attention on the concentrated object is called Dhyana."
Dhyana has been defined by the Samkhya school of Philosophy as "Dhyanam nirvishayam manah" which is translated as "the liberation of mind from all disturbing and distracting emotions, thoughts and desires." Dhyana always starts with Dharana, i.e. concentration; the mind becomes steady and one-pointed through concentration and when concentration leads to the uninterrupted flow of thought towards one object it becomes Dhyana.
The two Sanskrit words "Dhyana" and "Nididhyasana" both are sometimes used for Meditation, but there is a difference as "Nidhidhyasana" means "reflection or contemplation," a method used by Monastic tradition of Vedanta Philosophy. In comparison, Dhyana is a conscious and voluntary attempt made to still the activity of conscious mind. Through withdrawal of senses and concentration, one-pointedness of mind is achieved and it is then that the concentration is changed into meditation.
The relation between body and mind was widely accepted by the ancient scholars. It is a well-accepted fact that the regular practice of certain asanas, mudras, pranayama, dhyana etc. bestows remarkable changes in the physical and mental functions. The psychosomatic linkage is being increasingly recognized by the practitioners of modern medicine, in a sense that unless the mind is involved, the body cannot be treated and vice-versa.
Dhyana is an important Yogic technique. The regular practice of Dhyana brings many benefits to the practitioner - some direct and some indirect. It not only helps the practitioner to control many mental problems but also helps a person to attain the highest level of spiritual experience. Negative emotions like fear, anger, depression, stress & tension, panic, anxiety, reactions, worry etc are reduced and a calm state of mind is thus developed. Total personality and outlook of the aspirant changes for the better, so that he manages to face adverse situations in life in a better manner and discharge his duties more efficiently. The practice of Dhyana makes the person attain a positive personality, thoughts and acts. Dhyana also increases the concentration, memory, confidence, clarity of thoughts, and will-power.