Dhyana or meditation is defined by Patanjali as the uninterrupted flow of concentration of the mind on the object of concentration. The state of dhyana is an extension of dharana. There is a fine difference between dharana and dhyana. In dharana the mind continually tries to think of things other than the object, and the practitioner has to bring the awareness back to the object; distractions still exist in one form or another. In dhyana, however, the mind has been subjugated and is totally and continually absorbed in the object. It is in meditation that the deeper aspects of the object start to manifest themselves. The depth of concentration in dhyana is far greater than in dharana. It is through the regular and continual practice of concentration that dhyana spontaneously manifests itself.
Dhyana or meditation can be initiated in sitting in one pose and fixing the mind on an object, sound or breath. This leads to the free flow of thoughts, visions, memories etc. from the unconscious realms of mind and to probe the lower mind to remove the undesirable contents. When the lower mind has been fully explored, one can start to explore the superconscious realms to access the storehouse of knowledge, wisdom and energy within.
One can develop active meditational state in visualising, listening, reading and writing by regularly performing meditation in day to day yoga practice. This is in fact is the aim of yoga, to allow one to meditate while being involved in worldly activities. It does not mean that the activities will not be done, or not done with enthusiasm. In fact the work or external activities will be performed with more efficiency and energy.
Dr. Mahesh Chandra Panda