(Sanskrit आसन) Posture, seat, or position.
"For prayers and meditation, you can have any comfortable position. You must select a fine pose in which you can sit for a long time comfortably. The only condition is that your neck and back should be erect." —Swami Sivananda, Autobiography
"When you sit on the posture, think: "I am as firm as a rock". Give this suggestion to the mind half a dozen times. Then the Asana will become steady soon. You must become as a living statue when you sit for Dhyana. Then only there will be real steadiness in your Asana. In one year by regular practice you will have success and will be able to sit for three hours at a stretch. Start with half an hour and gradually increase the period. When you sit in the Asana, keep your head, neck and trunk in one straight line. Stick to one Asana and make it quite steady and perfect by repeated attempts. Never change the Asana. Adhere to one tenaciously. Realise the full benefits of one Asana. Asana gives Dridhata (strength). Mudra gives Sthirata (steadiness). Pratyahara gives Dhairya (boldness). Pranayama gives Laghima (lightness). Dhyana gives Pratyakshatva (perception) of Self and Samadhi gives Kaivalya (isolation) which is verily the freedom or final beatitude." —Swami Sivananda