Yoga is defined as a method – the process of nirodha (mental control) – by which union (the goal of yoga) is achieved. Yoga is therefore both the process of nirodha and the unqualified state of niruddha (the perfection of that process). The word yoga (union) implies duality (as in joining of two things or principles); the result of yoga is the nondual state..., or as the union of the lower self and higher Self. The nondual state is characterized by the absence of individuality; it can be described as eternal peace, pure love, Self-realization, or liberation.

The Yoga Sutras of Patanjali, Book I, 1999