"Under the radar" is an old military term. It comes from airplanes trying to fly real
low to the ground so that they would avoid detection by the enemy's radar. In Halo,
you can kind-of do the same thing. By pressing down on your left joystick, you
can go into a crouched position. Though you can't move around as fast, it allows
you to not be tracked on radar. So that you don't need to keep holding your joystick
down, you can go to settings and change the mode to toggle.
This video is about sneaking around undetected in the crouch position.
