The quintessential tanking cooldown, it greatly reduces the damage you will take for a limited time. Note that it does nothing to prevent tactical attacks or prevent damage from damage-over-time effects currently on you.
The Guardian's Belt legacy Guardian's Pledge Magnitude can increase the avoidance chance buff by up to 10%.
The Guardian weapon legacy Guardian's Pledge Cooldown can decrease the cooldown of this skill by up to 60 seconds. Some armour set bonuses also decrease the cooldown.