Meaning of Asana (Hatha Yoga Pradipika (1: 17))

Hathasya prathamaangatvaadaasanam pooroamuchyate.
Kuryaattadaasanam sthairyamaarogyam chaangalaaghavam.

Prior to everything, asana is spoken of as the first part of
hatha yoga.
Having done asana, one attains steadiness of body and mind,
freedom from disease and lightness of the limbs.

Asana means a state of being in which one can remain physically
and mentally steady, calm, quiet, and comfortable. In the Yoga Sutras
of Patanjali, there is a concise definition of yogasanas: “Sthiram
sukham aasanam”, meaning that position which is comfortable and
steady. So, we can see that yogasanas in this context are practiced to
develop the practitioner’s ability to sit comfortably in one position
for an extended length of time, as is necessary during meditation.
In raja yoga, asana refers to the sitting position, but in hatha
yoga, it means something more. Asanas are specific body positions
that open the energy channels and psychic centers. They are tools
to higher awareness and provide a stable foundation for our
exploration of the body, breath, mind, and beyond. The Hatha yogis
also found that by developing control of the body through asana,
the mind is also controlled. Therefore, the practice of asana is
foremost in hatha yoga.