In the ancient text on yoga by Patanjali, called the Yoga Sutras, there is a concise definition of yogasanas: Sthiram sukham asanam meaning ‘that comfortable and steady’.
Asana is to cultivating the inner connection between body, breath, mind, and soul.
Asanas means of enhancing the capacity of the body and mind so that a person could sit in meditation for long periods with as few distractions as possible. Only when the body is healthy and the mind one-pointed and inward does a person have a chance to discover the inner dimensions of life. This self-discovery is the essence of spiritual practice.
Deeper practices also involve an energetic experience - both during and after our practice. As we progress, we come to realize that the interior life of poses is the true nature of asana, and any sequence of postures can help awaken an experience of being within ourselves.