The meaning of yoga from Patanjali’s Yoga Sutras
(The Yoga Sutras are the most read yoga text. It was written approximately 2,500 years ago from a collection of ancient yoga knowledge that Patanjali gathered.)
The meaning of yoga from Patanjali’s Yoga Sutras is not the same as Hatha Yoga text. According to Pantanjali’s sources, yoga means concentration or samadhi. These full practices of yoga lead to samadhi. Yoga concentration is not on an object but is a quality of the mind. You move beyond to a state of no mind. Yoga does not begin until a person is able to concentrate. Asana is just stretching and pranayama just breathing exercises perhaps with the intent of trying for concentration.
Hatha yoga’s definition is another Sanskrit language breakdown meaning union. We can not have union because Prakruti (creation energy) must be separate from Purusha (consciousness/soul). However, it is true that we need union of the mind, body, and soul; so, the definition is correct in that way. We begin yoga with concentration and have the end goal of concentration.