An effect type. When a character uses a stance power, the character assumes a stance of some kind.
Duration: A stance lasts until the character assumes another stance or until the character falls unconscious or dies. A stance also ends at the end of the encounter, unless the stance can be assumed at will.
One per Turn: A character can assume no more than one stance per turn.
Published in Player's Handbook, page(s) 55, Player's Handbook 2, page(s) 220, Player's Handbook 3, page(s) 218, Rules Compendium, page(s) 120, 316.