Causes your attacks to ignore X% of your target's Armor and increases the damage dealt by your Rupture ability by Y%.
Serrated Blades is a 10 point talent in the Subtlety for Rogues. It was introduced in Patch 1.10 as a replacement for improved Rupture, and is a strict improvement over that talent. It is the pre-requisite for the 20 point talent Hemorrhage.
Serrated Blades is a passive ability that increases the rogue's damage output by allowing the rogue's attacks to ignore a small percentage of the target's armor. Also, the talent keeps the functionality of it's predecessor by increasing the damage of Rupture.
Rupture Damage Increase
As of patch 3.3.3, Serrated Blades ignore a percentage of the target's armour rather than a fixed amount.
(Below information may be out of date)
At level 70, Serrated Blades rank 3 will ignore 560 of the target's armor. This amount may not seem significant, but this is factored into every single attack, the benefit will add up.
At level 80, Serrated Blades rank 3 will ignore 640 of the target's armor per attack.