Dharana is the sixth limb of ashtanga yoga. It involves deep meditation where the object being focused on is held in the mind without consciousness wavering from it. Dharana means “holding steady”, “collection” or “concentration” of the mind

The basic idea is to hold the concentration or focus of attention in one direction. When the body has been prepared by asanas, the mind has been calmed by pranayama and the senses have been brought under control by pratyahara, the “seeker” reaches the sixth stage. dharana. Here, the mind has to be stilled in order to achieve this state of complete absorption.

The objective in dharana is to steady the mind by intently focusing on one particular activity of the mind. The more deep the focus, the easier other activities of the mind fall away. Now we can reach our greater potential for inner healing.

As the practitioner becomes more advanced, consciousness of the act of meditation disappears, and only the consciousness of being exists.

Want to know more? Read “Seeking Samadhi” by Judith Laseter at:
http://www.yogajournal.com/wisdom/461

Source: http://www.examiner.com/x-8997-Seattle-Yoga-Examiner~y2009m7d22-The-yoga-sutras-of-Patanjali-dharana