This thread has driven me to google 'yoga'. Mumsnet can do this to me while cooking 
So: the dictionary definition: "a Hindu spiritual and ascetic discipline, a part of which, including breath control, simple meditation, and the adoption of specific bodily postures, is widely practised for health and relaxation."
An actual Yoga site, however, describes it as this:
"Yoga is a Sanskrit word derived from the Sanskrit root “yuj” which means to connect, join or balance.
The most important thing, however, is that Yoga – with its entire applications and implications – is a powerful means to an end. The ultimate end of all human pursuits is “Moksha.” Moksha is freedom from all bondage; freedom from insecurities; freedom from the clutches of desires; freedom from the sense of limitations and inadequacy; freedom from all that thwarts us on our divine journey in life. In other words, the end of all human pursuits is everlasting peace, happiness and a sense of fulfillment. This is possible with steady and prolonged sincere practice of Yoga. It activates a process of cleansing and purification of mind, which in turn, prepares us for the dawning of Self-knowledge. Yoga means this connection; this knowledge that removes the impurities and the veil of ignorance that keeps us strangers to ourselves.
Yoga should never be mistaken for any other mode of exercise, which is operational only on a physical level."
So very supportive of what Lamaha says. My own yoga teacher is much like Lamaha describes - she calls yoga her religion, and is very much into the mind/body aspect.