After defeating the Colossus, Hayden gains the ability to throw up a protective shield that will rebound incoming projectiles back at enemies. At first you can only use it once before having to charge it back up, but as you progress, you can call on it three times in a row before having to regenerate it. The power is signified by one or three lights on Hayden's right shoulder.
The shield does not protect against attacks from behind or melee damage. It is also cancelled by shifting which also uses the same charge lights. Rebounding attacks at an enemy will also earn you the Rebound achievements.