Armor Lock was an armor ability in Halo: Reach. It basically freezes a player in place but makes them invincible for a short time. My experience had always been pretty terrible at using it efficiently. But I remember facing a ton of people who could use it like pros.
It was my least favorite ability in Halo: Reach, but I failed to realize it's ability to render a great weakness to vehicles. Any incoming air or ground vehicle that crashes into a armor locked player is basically toast. That would of been nice to know. Now I'm a little disappointed it got left out of Halo 4.