Ujyate anena iti yogah (Joining the individual soul to the universal soul.) – Classical definition.
Tam yogam iti manyante stiram inndriya dharanam (Yoga is holding the senses steady.) – Upanishad
Manh prasamano payah yogah (A technique to make the mind quiet is yoga.) – Yoga Vasista
Yogah chitta vritti nirodhah (Yoga is controlling the disturbances of the mind.) – Patanjali Yoga Sutra.
Samatvam yoga ucchyate (Yoga is a state of equanimity.) – Bhagvad-Gita.