What It Means:
Wikipedia: Dhāraṇā (from Sanskrit धारणा) is translated as "collection or concentration of the mind (joined with the retention of breath)" or "the act of holding, bearing, wearing, supporting, maintaining, retaining, keeping back (in remembrance), a good memory" or "firmness, steadfastness, ... , certainty." This term is related to the verbal root dhri to hold, carry, maintain, resolve. Dharana is the name.
Dhāraṇā is the sixth stage, step or limb of eight elucidated by Patanjali's Ashtanga Yoga or Raja Yoga. For a detailed account of the Eight Limbs, refer to the Yoga Sutras of Patanjali.
Dhāraṇā may be translated as "holding", "holding steady", "concentration" or "single focus". The prior limb Pratyahara involves withdrawing the senses from external phenomena. Dhāraṇā builds further upon this by refining it further to ekagrata or ekagra chitta, that is single-pointed concentration and focus, which is in this context cognate with Samatha. Maehle (2006: p. 234) defines Dharana as: "The mind thinks about one object and avoids other thoughts; awareness of the object is still interrupted."
Dhāraṇā, the sixth limb of yoga, is essentially concentration. It is the initial step in deep concentration, where the object being focused upon is held in the mind without consciousness wavering from it.
The last three limbs (Dhāraṇā, Dhyāna, and Samādhi ) are connected to ultimately achieve Samyama. In the former, the object of meditation, the meditator, and the act of meditation itself remain separate. The meditator or the meditator's meta-awareness is conscious of meditating on an object.
This limb can get overlooked as either unimportant or too difficult to bother with, especially since its fuller translation is “the binding of the mind to one place, object or idea.”
In yoga or in meditation, this limb can apply to concentrating on an intention, word, mantra or color.
For the individual, the way one’s mind concentrates determines to some extent what kind of person one is and what samskaras or psychic impressions are within oneself. The nature of the target one chooses also is a clue to one's inner make. Once the student enters into dharana, he can know his personal structure.