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A
softlock
is an instance where game remains in a playable state, but progressing further or past a certain point becomes impossible. It's an event that can happen to speedrunners where triggers and events are hit out of order, causing the games script to break completely, thus causing the progression breaker.
Contrast this with a
hardlock
, which locks up the game to the point where command inputs do nothing, and the game becomes unresponsive.