Ᾱsanam

A person seated straight-backed, cross-legged and with closed-eyes is considered to be in meditation. Is meditation the practice of a posture? Ᾱdi Śaṅkarācārya explains:

सुखेनैव भवेद्यस्मिन्नजस्रं ब्रह्मचिन्तनम् आसनं तद्विजानीयान्नेतरत् सुखनाशनम् ॥ ११२ ॥
सिद्धं यत्सर्वभूतादि विश्वाधिष्ठानमव्ययम् । यस्मिन्सिद्धाः समाविष्टास्तद्वै सिद्धासनं विदुः ॥ ११३ ॥

sukhenaiva bhaved-yasminn-ajasram brahma-cintanam, āsanaṁ tadvijānīyān-netarat-sukhanāšanam. siddham yatsarvabhūtādi viśvādhişthānam-avyayam, yasminsiddhaḥ samāviṣṭās-tadvai siddhāsanam viduḥ.

सुखेन – easily; एव – verily; भवेत् – becomes; यस्मिन् – where; अजस्रं – unceasingly; ब्रह्मचिन्तनम् – meditation on the Truth; आसनम् (इति)- to be posture; तत् – that; विजानीयात् – should know; न – not; इतरत्- any other, सुखनाशनम्-destroying happiness सिद्धम् – well known; यत् – which; सर्वभूतादि – the origin of all beings; विश्वाधिष्ठानम्- the support of the whole universe; अव्ययम्-immutable; (इति – thus); यस्मिन्- in which; सिध्दाः – Siddhas (the Enlightened ones); समाविष्टाः – completely absorbed; तत्-that; वै – alone; ( पण्डिताः – the wise); सिद्धासनम्- as siddhasana;  विदुः – know

112-113. One should know that to be a real posture, in which meditation on the Truth happens spontaneously and unceasingly and not any other that destroys one’s happiness. That which is well known as the origin of all beings and the support of the whole universe, which is immutable and in which the enlightened are completely merged – that alone is known as siddhāsana.

The seat on which we sit and the posture in which we sit are both called āsana. The scriptures give us guidelines as to where to sit, on what to sit, how to sit and thereafter what to do in meditation. One should choose a clean and quiet place, not too high (which can be precarious) nor too low or underground (which can be suffocating). The seat should be comfortable (should allow the body to remain straight and steady), act as a non-conductor of electricity (to prevent body energies from getting earthed) and protect from dampness.
A blanket with a cotton cloth over it will serve the purpose. According to the Yogasutras, ‘an āsana is a posture in which the body and mind remain still, steady and comfortable. Haṭha Yoga propounds 84 different postures, which help to keep the body fit, healthy and supple, and the mind pure and steady. Amongst these, some postures conducive for the practice of meditation are sukhāsana, padmāsana, svastikāsana and siddhāsana. An exercise focuses on the movement of the limbs. Ᾱsanas are not mere exercises, but practice of postures. It is a common misunderstanding that the mere practice of postures and some breathing exercises is Yoga. It should be noted that āsana is only one of the eight limbs of Aṣṭāṅga Yoga which presupposes the practice of yama (self-control), and niyama (discipline) as explained earlier and culminates in samādhi – absorption in the Self. Further one should practise Yoga as taught by a Guru established in Yoga (gurūpadiṣṭa-mārgeṇa yogam-eva samabhyaset). Following instructions from a book, a yoga practitioner got into a difficult posture and was unable to come out of it. Every move to extricate himself caused severe pain. Finally his friend had to call the author of the book to help him out! Initially, as we practise sitting in an āsana, there is some pain, discomfort and effort. With practice one can sit still, comfortably and effortlessly for a long time (prayatna-śaithilyāt anantya-samāpattibhyām). One accomplished (siddha) in āsana, remains unaffected by the pairs of opposites like heat and cold, pleasure and pain and so on. I knew a saint, who used to practise sitting still in his spare time after work. He was always calm and cheerful. He would advise all to remain still whenever possible. What should one do after taking care of one’s seat and posture? ‘With the senses and mind controlled, mind-intellect integrated, be focused on the Self.’ Remain seated undisturbed and unperturbed by situations (udāsinavat āsīnam). ‘One, who practises thus, remains effortlessly and comfortably in the Self, and is unshaken even by great sorrows or difficulties.’ Initially our focus is to maintain the body in a steady posture (āsana sthairyam), then we turn our attention to our mind. It should remain steady in a peaceful and happy state (sukha sthairyam). Thereafter, we attempt to make our contemplation on the Self or Truth (brahma-cintanam) steady (svarūpe sthairyam). This is termed as āsana – meditation. With practice, abidance in the Truth is effortless. To remain in that Truth in which accomplished (siddha) or Realised ones abide, which is the immutable substratum of the entire world and all beings, is called siddhāsana.