योगश्चित्तवृत्तिनिरोधः means - A process of blocking the patterns of Awareness, here I must be clear that - it means not the blocking of awareness but blocking of Patterns of it.
As in meditation - Awareness present but patterns is blocked/Absent.
When flow or PATTERNS of consciousness BLOCKED ,We can achieve different and fundamental state of consciousness.
CHITTA means INDIVIDUAL CONSCIOUSNESS. It includes- Consciousness state of mind + subconscious state of mind + unconscious state of mind.
Chitta = Pure Consciousness or = Individual Consciousness .
It includes 3 Types of Consciousness and 3 States of Consciousness .
Then one more question arise- what is mind???
Mind is just a instrument of knowledge, which see the chitta and perceive it according to choices/ stored samskara.
Another question- What is Consciousness???
Consciousness is unimaginable, beyond body, within this body ,some times outside this body ,it is infinite, unending or can say - Ananata . It is like a thread connecting many lives and incarnations .
For clearly understanding we must be know about -- What is Vritti ???
As we know Vritta means circle, hence vritti means circular, as waves in still / pond water.
Chitta vritti = Attitude of chitta or we can say modes of mind .
Blocking of the patterns arising in all the dimensions of Consciousness and due to this blocking expression of individual awareness (arising in different places) transcended .
Because there is 5 stages of Mind (according to PYS) and 5 Types of Vritti . once they block one by one ,we can reach step by step at the stage of samadhi or merge with super Consciousness. The final AIM of YOGA.