This is a question that is quite vast and there are so many ways this can be open to interpretation, what is yoga? Well I will share with you from my perspective what yoga is...whether that is right or wrong it is true for me right now, and is always open to changing.
The word yoga itself comes from the Sanskrit word 'yuj' which means 'to yoke' this is the marriage of the body, breath and mind. Yoga is a scientific ancient sacred practice of not solely the physical, but also a way of life to be lived through every aspect of life. It has been interpreted by some as 'unification with the divine/supreme', this is the ultimate goal of a yogi, oneness with the divine (or God).
Developed over 5000 years ago, yoga was practiced during Vedic India, some of the earliest sacred texts collectively known as 'Vedas' have been dated as early as 1700BCE. These texts provide a philosophical, moral and religious underpinning of this ancient practice, and ultimately how we should be living our lives.
In the west, the biggest focus of yoga has often been the physical or asana practice, whereas in the origins of yoga this is noted as just one of the core elements, based on a deeper philosophy. The 8 limbs of yoga set out by Patanjali in his Yoga Sutras (divine laws of yoga) provides a wheel of which sets out the elements which make up Yoga.
Yamas are a moral code for how we should live, the yamas are made up of: ahimsa (none violence); satya (none lying); asetya (none stealing); brahmacharya (none waste of vital energies) and aparigraha (none greed).
Nyamas are linked to our personal conduct as an individual: saucha (purity); satosha (contentment); svadhyaya (self study); tapas (discipline) and ishvara (surrender).
Asanas are the physical posture of yoga, the physical practice of moving the body, this is only one aspect of the yoga.
Pranayama the control of the breath, the mastery of the breath and the mystery of the breath. Yogi's believe that the breath is the lifeline to God, not only rejuvenating the body, the practice extends the life of a practitioner.
Pratyhara is the withdrawal of the senses, the awareness of our senses but gaining the ability to direct this awareness internally and not within the stimuli of the world around us.
Dharana is one pointed focus or concentration, following on from pratyhara and prior to beginning meditation, dharana begins to work on the stillness in the mind through focus - this may be focus such as a chakra or the white light.
Dhyana relates to the practice of meditation an observation of the mind and breath. The ability to be aware without a focus. A somewhat difficult task for many of us with our busy minds - however this wheel outlines the journey of true yoga.
Samadhi which is the state of pure bliss, the overall goal, to reach unity with the divine God. Also known as the transcendence of the self or what some will refer to as enlightenment, this state of ecstasy is only achieved once the body, mind, breath and soul have been purified and brought into alignment with God. Samadhi is something which can only be achieved through devotion.
The path of yoga is not linear; it is a journey a winding road which throws up all kind of hurdles along the way. The physical practice of asana allows for us to reconnect with the physical body, through my own personal practice with my teacher this then allowed me to open up to my emotional self and begin a journey of emotional healing. This, in essence, is what the physical postures are designed to do, they are designed to unlock the binds which are held within the body...these binds, tensions, rigidity can be directly linked to our emotions.
Therefore, when the emotion is acknowledged, felt and released it is possible that the tension and block in the body will be eased and released. One cannot simply occur without the other in the long run. This is also the way in which dis-ease is eradicated and prevented within the body, through the feeling and healing of emotions. A process very much bypassed through many practices, with a focus being on positive thinking and letting go.