Asana is the third limb of the eight limbs of yoga as extolled by [wiki]Patanjali[/wiki] in the [wiki]Yoga Sutras[/wiki]. It is the yoga poses or postures.
Patanjali’s deeper frame of reference suggests that he is referring to the steady and comfortable postures of all the three bodies, physical as well as astral and causal so that they will unhinge the awareness locked in them to pave the way for dharana, dhyana and samadhi.
In Raja Yoga, Asana means a sitting posture. Of course, a sitting posture meant for meditation. But in Hatha Yoga, Asana is more than that. It extends to mean other postures also like back bending, forward bending, and inverted postures.
The Sanskrit word Asana means "a seat." Understandably, the word was initially used to mean a sitting posture only. That was why earlier Raja yoga or Ashtanga Yoga used the term to mean a seat. After the advent of Hatha Yoga, the extensive meaning came in place.Patanjali defines Asana in two verses that include three terms. sthira-sukham-āsanam prayatna-śaithilya-ananta-samāpatti-bhyām Here is [the complete guide on Asana](https://www.classicyoga.co.in/2019/08/asana-in-yoga/)
Asana is used as a suffix in the Sanskrit names for yoga poses, such as trikonasana, virabhadrasana, and eka pada rajakapotasana. Knowing this and a few other Sanskrit terms can help you unravel these complicated names. For instance, eka pada means one footed, so in these poses, you can expect that one foot will be doing something different from the other. Parsva means side (usually a pose facing one side), parivrtta means turned (usually a twisted version of a pose), and so on. Beginning to see these patterns helps the names start to make more sense.
What most people call yoga could more specifically be called asana. Yoga has eight limbs. Besides asana, yoga also encompasses pranayama (breathing exercises), dhyana (meditation), yamas (codes of social conduct), niyamas (self-observances), pratyahara (withdrawal of the senses), dharana (concentration), and samadhi (bliss).