The "RS" button on an Xbox controller stands for "Right Stick". It is located on the right side of the controller and is used as a small joystick for interacting with games and the Xbox console. It can also be clicked to activate a button function. In some games, the "RS" button is used to re-center the camera or to strafe or move sideways. The "LS" button, located on the left side of the controller, is the Left Stick and is used for navigation and interaction with games, apps, and the Xbox console.