Dhyāna has in today’s world come to mean meditation. In fact, dhyāna is a highly esoteric yogic practice, not apparent to most. Sage Patañjali enlists dhyāna as one of the eight limbs of asṭāṅga yoga. It is only after practicing and perfecting the limbs of yama, niyama, āsana, prāṇāyāma, pratyāhāra and dhāraṇa, can a yogī establishes himself in the practice of dhyāna. Perfection in dhyāna in turn, results in the stilling of the mind, a state referred to as samādhi.
Maharṣi Patañjali defines Dhyāna thus –
तत्र प्रत्ययैकतानता ध्यानम् ।
tatra pratyayaikatānatā dhyānam ।
[Patañjali Yoga Sūtra, 2.3]
There, a continuous single-stream of cognition is called meditation.
Meditation is the stream of cognition (pratyaya) focused on the object of contemplation (dhyeya.) The stream of cognition must be incessant, steady, and unmoved by interruptions. Such a practice of dhyāna, states Maharṣi, leads the practitioner to samādhi (absorption) and enables yoga (union.)
The Agni Purāṇa explains dhyāna as follows,
ध्येयावस्थितचित्तस्य प्रदेशे यत्र कुत्रचित् ।
dhyeyāvasthitacittasya pradeśe yatra kutracit ।
[Agni Purāṇa, 374.4]
Meditation is defined as contemplation, where the mind is firmly and incessantly fixed on the object of contemplation.