In the West, yoga has come to mean the physical postures known as asana. But in the tradition that gave us yoga, the term actually refers to an inner experience gained during meditation: yoga means union or the state of unified awareness.
From the Yoga Sutras of Patanjali:
yogaś citta vṛtti nirodhaḥ
"Yoga is the cessation of the thought waves of the mind."
The Transcendental Meditation technique is yoga practice in the purest sense. It is a technique for arriving at the "cessation" of mental activity while maintaining inner wakefulness, the state of pure consciousness or samadhi. This experience is the true state of yoga. (2:46)
Read: The True Nature of Yoga: Stretching the Boundaries of Consciousness