Boundaries, forbidden areas, ceilings, out of bounds are all terms for parts of a map that can only be traveled into for a short period of time. These areas are often displayed on the mini map, and in the case of the ceiling, displayed on the aerospace HUD. Once in one of these areas a timer will start, usually between 8 and 20 seconds. Sometimes players will have a few seconds more than what is displayed to return to the normal playing area of the map, other times death is instantaneous when the timer reaches zero. Ceiling timers and horizontal map boundary timers are not always the same. Ceiling timers are usually much shorter than other boundaries. Players should avoid going out of bounds because of the possibility of death for doing so as well as the annoying timer that appears on the screen. The timer covers part of the reticle and has a low transparency, this makes aiming very difficult while out of bounds.
Going out of bounds, temporarily, can be an effective way to shake off pursuers. Occasionally, going out of bounds is a shortcut for aircraft, like in E7 on TC StoneRose.