"The posture for yoga should be steady, stable, and motionless, as well as comfortable."
(sthira sukham asanam)
― Patanjali‘sYoga Sutras, 2.46-2.48

Sthira – to be conscious, steady, alert, present, firm, stable
Sukha(m) – to be relaxed, happy, gentle, at ease, comfortable, soft
Asanam – yoga posture, way of sitting, being seated, place

A posture is a life situation. Once you are into it, settle in, go through it. Observe the cues rendered by your body and your mind, and accept them without judgment. Are you breathing or are you withholding your breath? Is your body tensed or relaxed? Is your mind calm or racing? Challenge your awareness by finding the balance between effort and ease.