Yoga Sūtra Chapter Three verse 2
tatra pratyaya-ekatānatā dhyānam ||2||
There, the continuity of psychic activity is meditation.tatra - therepratyaya - psychic activityekatānatā - continuitydhyāna - meditation; mental representation of the personal attributes of a deity
Commentaries and ReflectionsT Krishnamacharya:TKV Desikachar:
“Prāṇāyāma leads to this.
Pratyāhāra, to see without the senses distracting or pulling the mind, and
Dhāraṇā, to see without the mind losing itself, because of colouring or expectations.
Dhyānam arises out of this.”
“Perhaps the best explanation of Dhyāna is given by Patañjali in the Yoga Sūtra Chapter Three verses One and Two, where he states that one must first fix the question (Dhāraṇā) and then link to it (Dhyāna).
One who is not able to fix the question is not able to succeed in Dhyāna.”
“Dhāraṇā is the process of ‘holding onto’ the object.
Dhyānā is the process of ‘linking with’ the object.
Samādhi is the process of ‘integration into’ the object.”
Reflections on Yoga Sūtra Chapter 3 verses 1-3