The word yoga comes from the Sanskrit root, yug, which is to yoke, bind or merge. Yoga is the binding or merging of what has been perceived to be separate, but in fact, is not. There are schools of philosophy in yoga as there are in psychology and religion, some of which are dualistic and some non-dualistic. That transcendence comes through a merging with the godhead, a dropping of ego and separateness in the moment- an instantaneous recognition that consciousness is both God and the illusion of everything else. Yoga is known in the Western world primarily as a form of physical exercise using breath control.
Yoga is said to have many paths.
Four of these ways or limbs of yoga are jnana yoga, the way to God through knowledge, bhakti yoga, the way to god through love, karma yoga, the way to God through work, and raja yoga, the way to God through psychophysical experience. Yoga has lasted thousands of years as a world view, as a science and art of living, because Yoga works. There has been a mountain of written material published about yoga, but one will not understand yoga until one practices some means of hatha yoga. The way to the subtle is through the gross, as the way to understanding the psyche is through the emotional realm felt through the physical body. Yoga is practical.