Soft lock
Also said as Softlock, Unwinnable state, Dead end
The game is still running and you can still move, but you can no longer finish it, and it does not tell you. A hard lock is the frozen version, where nothing responds at all.
A player may lose hours before they find out, and all they can do is reload an old save. Few things break trust as completely. Anything that can be spent, destroyed or left behind has to be checked for it.
Say it
“Small keys are consumed, so check the dungeon can't be stranded: count doors against keys in every order, and if a player can run out, put a spare in a chest that refills.”
Where you’ve seen it
Sierra adventures such as the King's Quest series could strand you hours after you walked past an item you could no longer go back for. Ron Gilbert's 1989 essay Why Adventure Games Suck told designers never to require such an item.
Not to be confused with hard lock
A hard lock is a crash: the program has stopped. In a soft lock the program is fine and the player is the one who has been stranded.