A sudden win is an early or false form of victory during Zombie Escape which involves killing all the remaining zombies before the end of a playround in a single instant.
Sudden wins are commonly found on maps which allow for a very small amount of motherzombies to spawn (usually one or two only) that can be killed by the humans without being able to zombify any player in time. Players that kill these zombies before the map starts are also called 'zombie hunters'. On some maps special items can also cause all of the zombies to die from the effect they may cause.
Ze FFVII Mako Reactor is a perfect example of where a sudden win can happen. The Ultima Materia is a special item that will detonate any zombies in range after a specific timer and with a bit of luck, if all zombies are within its range, they will all die instantly, causing a sudden win.
Ze Predator Ultimate has the gauss rifle, another special item that causes all zombies to die that touch its ray of light when fired. If by any chance all zombies are in the Line of Sight of the gauss rifle, they will all die causing a sudden win