Split screen
Local multiplayer where the screen is carved into two to four panes and the scene is rendered once per player.
Each player gets their own camera and viewport, and the engine runs the whole pipeline — frustum culling, sorting, draw calls — once per pane. Four players means close to four times the work on a quarter of the pixels each, so developers cut draw distance and detail to keep up. GoldenEye 007 (1997) and Halo (2001) made the four-way split the centrepiece of couch culture.
The social side effect was "screen watching": your opponent's view sat half a metre away, and peeking was half the strategy. As online play took over in the 2010s the mode quietly vanished from many series, partly because it is a lot of work for an audience that increasingly plays alone.