Unchained is a star within the Constellation The Lady in Elder Scrolls Online.
This was added in Update 6 with the Champion System. It reduces the Stamina cost of abilities by 80% for 3 seconds after breaking free of a stun, knockdown, fear, disorient or stagger. 120 points in the Lady Constellation are required to unlock it. Once unlocked the player will acquire this bonus automatically and across all characters on their account.