This is the main verse in definition of what yoga is in Patanjali Yoga Sutras……. “YogasChitVritiNirodhah” = Yoga is detention of vrittis from chitta.
Chitta is an inner organ that is very difficult to explain. Chitta is the instrument or medium through which the small self materializes ones individual world, lives and evolves in the world until they have become perfected and united with the Absolute. When the consciousness associates with prakrtiti (material nature in its germinal state, eternal and beyond perception), chitta comes into action. Chitta associates with with every moment and instant of the event. Chitta is the reservoir of karma, experience, tendencies and everything that happens in that interaction between soul and prakriti. Chitta captures everything. The vritti is that information captured. The reactions are these chitta vrittis. We cannot know what this state of Self-realization is as long as we are involved in the play of ChittaVrittis. It can only be realized from within and not comprehended from without. When the Citta Vrttis are not in the state of Nirodha (extinction of feeling and perception, the containment of the modifications of the mind), one is assimilated with the particular Vrtti which happens to occupy the field of his consciousness for the moment. The state of self realization is yoga. Nirodha and Yoga are the same.