Asana, Sanskrit for "sitting posture" (asanam is 'sitting' or 'as' / aste is 'he sits'), is a body position, typically associated with the practice of Yoga, intended primarily to restore and maintain a practitioner's well-being, improve the body's flexibility and vitality, and promote the ability to remain in seated meditation for extended periods. In the context of Yoga practice, asana refers to two things: the place where a practitioner (yogin (general usage); yogi (male); yogini (female)) sits and the manner (posture) in which s/he sits. In the Yoga sutras, Patanjali suggests that asana is "to be seated in a position that is firm, but relaxed". As the repertoire of postures has expanded and moved beyond the simple sitting posture over the centuries, modern usage has come to include variations from lying on the back and standing on the head, to a variety of other positions.In the Yoga sutras, Patanjali mentions the execution of an asana as the third of the eight limbs of Classical or Raja yoga.
The word asana in Sanskrit does appear in many contexts denoting physical position, although, as noted, traditional usage is specific to the practice of yoga. Traditional usage defines asana as both singular and plural. In English, plural for asana is defined as asanas. In addition, English usage within the context of yoga practice sometimes specifies yogasana or yoga asana, particularly with regard to the system of the Ashtanga Vinyasa Yoga. That said, yogasana is also the name of a particular posture that is not specifically associated with the Vinyasa system, and that while "ashtanga" (small 'a') refers to the eight limbs of Yoga delineated below, Ashtanga (capital 'A') refers to the specific system of Yoga developed by Sri Krishnamikurti at the Mysore Palace.
Third of the Eight Limbs
In the Yoga Sutra, Patanjali describes asana as the third of the 8 limbs of classical, or Raja Yoga. Asanas are the physical movements of yoga practice and, in combination with pranayama or breathing techniques constitute the style of yoga referred to as Hatha Yoga. In the Yoga Sutra, Patanjali describes asana as a "firm, comfortable posture", referring specifically to the seated posture, most basic of all the asanas. He further suggests that meditation is the path to samadhi; transpersonal self-realization. 
The eight limbs are, in order, the yamas (restrictions), niyamas (observances), asanas (postures), pranayama (breath work), pratyahara (sense withdrawal or non-attachment), dharana (concentration), dhyana (meditation), and samadhi (realization of the true Self or Atman, and unity with Brahma (the Hindu and Vedantic interpretation of god, also the Taoist Supreme Ultimate, the Judaic Yahweh, the Islamic Allah, or simply the Godhead, etc.)).
- Feuerstein, Georg (1996). The Shambhala Guide to Yoga. Shambhala Publications, Boston. pp. 26
- "Patanjali Yoga sutras" by Swami Prabhavananda , published by the Sri Ramakrishna Math ISBN 81-7120-221-7 p. 111
- Verse 46, chapter II; for translation referred: "Patanjali Yoga Sutras" by Swami Prabhavananda , published by the Sri Ramakrishna Math ISBN 81-7120-221-7 p. 111
- Patanjali (± 300-200 B.C.) Yoga sutras, Book II:29
- Arya, Pandit Usharbudh (aka Swami Veda Bharati) (1977/1985). Philosophy of Hatha Yoga. Himalayan Institute Press, Pennsylvania.
- Swami Prabhavananda (Translator), Christopher Isherwood (Translator), Patanjali (Author) (1996, 2nd ed.). Vedanta Press.