Asana can be defined as a physical Yoga posture or position that is designed to help master the body and enhance the body's functions.
Yoga poses are, in essence, Yoga exercises creating strength and endurance, improving circulation and energy flow, cleansing organs and other systems, and expanding muscles and joints. With all these benefits of the Yoga poses, we can not lose attention to the original purpose of the Yoga pose or Yoga exercise.
Yoga exercises evolved thousands of years ago from the need to create a healthy body in order to move more readily to the state of oneness and realization. When the body is cluttered with stress, tension, and disease, this clouds the mind and the ability to connect with the inner self. The physical freedom attained from the Yoga exercises increases one's ability to sit with silence and joyful observation.
The practice of Hatha Yoga (Yoga exercises) can be easily moved into a state of Ego where one drives expectations and goals into the Yoga poses. Rather than connecting with in the Inner Self, the practice of Yoga exercises moves one deeper into the physical reality of disillusion.
Western culture has easily turned Yoga exercises into another form of superficial workout routines and, rather than having a holistic connection, many people are moving to a place of obsession with the body and its' achievements. Asana can be described as a physical state of the body such that the posture moves one into an existence of wholeness and steadiness allowing one to reflect inwards on the entire being.
This state of steadiness involves no goals, no future, and no analyzing - just observing the how the physical self receives vitality and openness enabling the mind to explore clarity.