Yoga means union or the act of uniting and connecting. It is derived from the etymology of the root word yuj, meaning to yoke or join. In the context of the philosophy of Yoga this is the joining of the individual self ([wiki]atman[/wiki]) with the univeral self ([wiki]brahman[/wiki]) which can also be interpreted as joining the soul with god. However, a more secular interpretation is the joining of the mind, body and soul or self-realization. In other words, Yoga is any practice which brings one into union with their true self or restores them to their original and pure state of harmony.
It is often misunderstood that Yoga means to merge with god, but this is not strictly true, but only an interpretation of one sect of a school of Hindu philosophy called [wiki]Vedanta[/wiki], known as [wiki]advaita[/wiki] (non dualism). Other sects such as [wiki]dvaita[/wiki] (dualism) and [wiki]visheshadvaita[/wiki] (special non dualism) interpret yoga as either having a revelation of god or becoming one with god.
Another very popular definition of Yoga is given by [wiki]Patanjali[/wiki] in the second sutra of the [wiki]Yoga sutras[/wiki], “Yogas chit-vritti nirodha” meaning Yoga is the cessation of the modifications of the field of consciousness. These modifications are known as [I]chit-vrittis[/I] roughly meaning thought waves or thought activity. In other words the total stilling of the mind is Yoga. This leads to the goal of Yoga which is union with the self. Patanjali’s definition can be regarded as a scientific definition of what Yoga is doing at the process level.