Dhyana (ध्यान, Dhyāna)
While the dictionary meaning of Dhyana is profound meditation or concentration, in Yoga parlance, it is actually the seventh limb or constituent part of Ashtanga-yoga (अष्टाङ्गयोग, Aṣṭānga-yoga) as given by Patanjali (पतञ्जलि, Patañjali) (1):
Yama (यम, Yama), Niyama (नियम, Niyama), Asana (आसन, Āsana), Pranayama (प्राणायाम, Prānāyāma), Pratyahara (प्रत्याहार, Pratyāhāra), Dharana (धारणा, Dhāranā), Dhyana (ध्यान, Dhyāna) and Samadhi (समाधि, Samādhi) are the eight component parts of Yoga.
Dhyana according to Yogasutra:
After defining Dharana , in the very next Sutra, Patanjali defines Dhyana thus (2):
तत्र प्रत्ययैकतानता ध्यानम्|
tatra pratyayaikatānatā dhyānam |
"Then (i.e after perfecting Dharana) the mental activities form an uninterrupted flow only in relation to this object".
Once the direction is fixed, a link develops between the mind's activities and the chosen object (3).
Dhyana according to Yogayajnavalkya Samhita:
The great Yogi Yajnavalkya states that Dhyana is the means for liberation from bondage (4). He defines Dhyana thus (5):
ध्यानमात्मस्वरूपस्य वेदनं मनसा खलु |
dhyānamātmasvarūpasya vedanam manasā khalu |
"Dhyanam (Dhyana) helps the mind to know the true nature of the soul or Atma.
Further Yajnavalkya classifies Dhyana in to two types namely: Saguna (सगुण, Saguna) and Nirguna (निर्गुण, Nirguna). He states (6):
सगुणं निर्गुणं तच्च सगुणं बहुशः स्मृतम् |
saguṇaṁ nirguṇaṁ tacca saguṇaṁ bahuśaḥ smṛtam |
Dhyanam (ध्यान, Dhyāna) is classified as Sagunam (सगुण, Saguna) and Nirgunam (निर्गुण, Nirguna). Sagunam (Saguna) is more acclaimed.
(1) Yogasudhakara, A commentary on Patanjali's Yogasutra by Sri Sadasivendra, Sadhana-pada, Sutra number 29.
(2) Reflections on Yogasutra-s of Patanjali, by TKV Desikachar, Sutra III.2, the actual Sutra and translation.
(3) Reflections on Yogasutra-s of Patanjali, by TKV Desikachar, Sutra III.2, TKV Desikachar's comments to Sutra III.2.
(4) Yogayajnavalkya Samhita, Translated by TKV Desikachar, Chapter Nine, verse IX.1, page 119.
(5) Yogayajnavalkya Samhita, Translated by TKV Desikachar, Chapter Nine,first half of verse IX.2, page 119.
(6) Yogayajnavalkya Samhita, Translated by TKV Desikachar, Chapter Nine, second half of verse IX.2, page 119.