Yōga Sūtra 1.02

योगश्चित्तवृत्तिनिरोधः।

yōgaścittavr̥ttinirōdhaḥ।

[योगः चित्त वृत्तिः निरोधः।
yōgaḥ = Yōga is; citta =consciousness; vr̥ttiḥ = engaging in activities; nirōdhaḥ = restraining of;]

Yoga is restraining activities of the consciousness (Chitta).

Sometimes we are aware of what we are doing, and we say we are conscious. E.g. At the beginning of a music concert, when musicians are still settling down, you are aware you have come there to listen to music and you can see and observe various musicians tuning their instruments. But, most of time you are engaged in activity (vritti) and you are not consciously aware of what you are doing. E.g. You are listening and enjoying music, and you really don’t make a distinction between you listening the music and the music itself. Yōga is a disciple to restrain the consciousness, so that it does not turn itself into involved activity where you lose your awareness. Being aware all the time is goal of Yōga.