Evasion

Evasion is a level 8 Assassination and Subtlety rogue ability. It is one of the Rogue's defensive abilities, boosting their dodge rate by 100% for 10 seconds.

Tips and tactics
Won't let you dodge attacks made from behind, and does not work at all when you're stunned. Choose the right moment to use it, as most melee classes can counter it with non-melee-based attacks: paladins can stun you with Hammer of Justice, druids can root you with Entangling Roots, Outlaw and Subtlety rogues can use Blind, etc. At higher levels you can benefit from either Cloak of Shadows, but keep this in mind anyway.

In any melee situation, it will significantly lessen the damage you're taking.

Using Evasion during certain raid encounters can be key to your raid's success.

If your tank dies when the boss is almost dead, Evasion may be a lifesaver. Pop Evasion as soon as you see that the boss targeted you. You can now tank the boss for 10 seconds, which might just give enough time to kill the boss. Vanish just before Evasion ends. If there is more than one rogue in the group or raid, you may chain Evasion-tank the boss, giving even more time to DPS.