Frame skip
Skipping the drawing of some frames when the machine can't keep up, so the game runs at the right speed even when it looks choppy.
When rendering can't keep pace, you have two options: slow the whole game down, or let the simulation keep ticking at the correct rate and simply not draw some frames. The second is frame skip. Logic, physics and the clock run on; only the picture skips.
Emulators lean on it heavily — a weak host can run a game at full speed by drawing every other frame. The alternative, letting everything crawl, is the spiral of death you hit with a fixed timestep once each frame takes longer than it has. The trade is clear: frame skip preserves pace and input response at the cost of smoothness. The player sees the stutter, but is spared the feeling of wading through treacle.