English definition: Seat, posture
How we use the term in yoga: Pose, steady and comfortable posture.
Literally “seat,” it is implied that this seat is one that is both steady and easy, meaning that the body has found a balance of strength and suppleness that allows for a supported and effortless posture. While originally this may have referred just to a seated posture for meditation, today we use it to refer to any posture we put the body into during a yoga practice. The goal of a balance of strength and ease remains, regardless of the position or sequence of positions (i.e. body in motion).
The definitions I offer here are pulled together from my practice and study of yoga. I welcome friendly dialogue on the explanation of any term!