There are many definitions of yoga.

1. Yoga means “union” or “connection.” In Sanskrit, the word “yoga” is used to signify any form of connection, for example between two planets in a horoscope. In a philosophical sense, however, yoga means the conscious connection of the little egoic self with the greater Self. Conscious connection to something allows us to feel and experience that thing, person, or experience. Humans seek connection because it is ultimately fulfilling. To not be connected is to be disconnected, and disconnection is the source of our greatest pain. It leads to loneliness and alienation.
2. Yoga is a science, that is, it is a body of techniques that lead us to consciously connect with ourselves and with life. It is also the actual experience of connection that results from practicing the techniques. There are many traditional yogic paths that facilitate connection to the highest truth and awaken our own consciousness. These systems, such as tantra, mantra, laya, kundalini, bhakti, jnana, karma yoga, and so on, give us the tools to achieve higher knowledge and the experience of connection. They are suited to different personality types. They allow each one of us to access our own truth and to arrive at that truth by our own means, through our own chosen path. It is very important as yoga teachers to be totally respectful of every path.
3. The great sage Patanjali, in the system of Raja Yoga, gave one of the best definitions of yoga. He said, “Yoga is the blocking (nirodha) of mental modifications (chitta vritti) so that the seer (drashta) re-identifies with the (higher) Self.” Patanjali’s system has come to be the epitome of Classical Yoga Philosophy and is one of the six or seven major philosophies of India. It is a very formal definition that expresses an ultimate aim in yoga. Though few people ever attain total re-identification with the Self, the journey towards this state is in itself very fulfilling. In fact, Patanjali’s system of yoga is the basis of yoga psychology: the process of transformation of the limited, dull, and ignorant mind into a self-effulgent, powerfully creative force for higher living.
4. The definition of yoga in the Hatha Yoga texts is the union of prana (the upward force) and apana (the downward force) in manipura chakra (at the navel center). Hatha yoga teaches us to master the life force of prana. By learning how to feel and manipulate the life force, we access the source of our being. If prana and apana can be united in manipura chakra, we can awaken a very powerful energy which leads to the attainment of Raja Yoga, self-realisation. Chapter 1, verse 41 of the Hatha Yoga Pradipika states, “When perfection is attainable through Siddhasana (a powerful meditative posture), what is the use of practising other asanas? When the flow of prana is stabilized, the breath stops spontaneously (kevala kumbhaka) and a mindless state (unmani) arises spontaneously.”
5. The definition of yoga in Kundalini Yoga is the union of ida (the mental current) and pingala (the pranic current) in ajna chakra (the third eye). Yoga aims to unify duality in us by connecting body and mind. This leads to the experience of the absolute, transcendent, higher Self.
6. My favourite definition of yoga is that it is any method that allows us to wake up to who we really are and to what life is all about. Anything that allows us to be more aware of ourselves and to feel connected to ourselves and life is a form of yoga. It could arise from having a cup of tea, as is done in Japan in formal tea ceremonies. Or it could be the sense of connection that comes from doing something you enjoy like sports or gardening. Everything we do can become yoga if it is done with awareness. Awareness is the key. Awareness allows us to feel and experience connection. Without awareness we could be connected and not even know it. So when we teach yoga, if we are emphasizing awareness rather than just technique, we are supporting the student’s growth both inside and outside of the classroom.