From The Heart of Yoga: Developing A Personal Practice by T.K.V. Desikachar:

"There are many definitions of yoga...

• yoga as the movement from one point to another, higher one
• yoga as the bringing together, the unifying of two things
• yoga as action with undivided, uninterrupted attention

These definitions of yoga have one thing in common: the idea that something changes. This change must bring us to a point where we have never been before. That is to say, that which is impossible becomes possible; that which was unattainable becomes attainable; that which was invisible can be seen."