The first is “Yogash Cittavrtti Nirodhah” which means “Suspension of mental tendencies is Yoga”.
This definition tells us that the true self is what remains when the noise and activity of the mind have been suspended or turned off. The waves of mental activity are like a curtain which hides the inner self. By calming and ultimately suspending these mental waves we can uncover the true self.
The second definition is “Yogo Samyogo Ityukto Jiivatma Paramatmanaha” which means “Yoga is union between the individual self and the Cosmic Self (God)”.
(Note: Yoga explains that as God is the center of everything He must also be the center, or “Self”, of every human being. Thus, the individual selves are many but the Cosmic Self is one). This definition goes further than merely calming the mind. Here the goal is to unify the small self with the Cosmic Self – or the lower self with the Higher Self. Such oneness is achieved as a result of sustained and loving concentration on the thought of the Cosmic Self. By combining these two traditional definitions we can conclude that all practices which calm and control the body and mind and help to focus the attention on the Cosmic Self are Yoga.
Mind, body and spirit are inseparably connected. Therefore to achieve self-realization it is necessary to integrate physical, mental and spiritual practices. Yoga practices for developing the body include yoga exercises (Asanas) and diet. Yoga practices for developing the mind include following moral principles, breath control, sense withdrawal and concentration. Yoga practices for spiritual development include meditation and contemplation, contact with spiritual people and serving others. Putting it all together we can summarize Yoga as a system of physical, mental and spiritual practices whose aim is self-realization.