Input delay
The netcode technique that deliberately holds back your own button presses by a few frames so the opponent's arrive in time and everyone simulates the same frame at once.
In a deterministic lockstep game every machine must compute exactly the same frame, but the network takes time. The answer before rollback was to delay even the local player's input by a few frames — just long enough for the remote presses to arrive — so nobody has to guess or rewind. The price is a felt lag between button and action, worst over long distances, which is deadly in fighting games. That very pain pushed Tony Cannon to build GGPO (2006) and popularise rollback netcode, which predicts and corrects instead. Delay-based netcode survives anyway, simple and exact.