These are codes you enter in the Halo Waypoint app.
To enter them, you Press "X" which brings you to the classified section.
Then you press "X" again to enter a code.
NOTE: The raider armors can't be unlocked until you have beat the Spartan Ops missions.
I will update once they complete codes.
The people who found the codes are from the Halo Waypoint forums.
Picture from: Here