Exits are the point of the level where the player (actively or passively) gains access to the next level.
Doom Exit Door

An exit door in Doom classic.

Exit triggers can have many forms: specials sectors, linedefs or scripted actions. Visually, most of the exits are switches, bottomless pits over hell, teleport pads or special doors.The exits have changed appearance over the course of the Doom games, from the original exit doors of Doom (featured to the right) to the varying exits in Doom (2016). They are usually followed by a screen reflecting over the player's performance that level.