Yoga is defined as union, a union between individual existence and its source, the supreme existence. It is to make you realize your identity with the greater self, and also to make you know and tune in with your existing inner nature. Yoga also is a systematic science, its teachings are an integral part of most religions but yoga itself is not a religion.

Most religion teaches what to do but yoga teaches how to be. These definitions of yoga are just a purely spiritual one. There are so many other definitions as well which also apply to all the levels of existence and awareness. For example at physical level most people have a body that is continually in a state of disruption with their inner organs, muscles and nerves no longer harmonize and assist each other.

Yoga aims at bringing these things in a perfect coordination. So another definition of yoga is physical harmony and health. And at mental level many people suffer from mental disturbances in the form of conflicts, neuroses, phobia and so on, which can make them unhappy and depressed in their life. Here yoga aims to smooth out and eliminate mental problems. So yoga can also be defined as mental balance and mental peace.

So we can say that by yoga we can work on the three aspect of human life as spiritual, physical and mental level.