I mean some sort of game-regulated countdown or measure that leads to consequences. Eg each action takes a turn, and a torch burns for 4 turns (light clock *); each action takes a turn, and every 4 turns the GM rolls for wandering monsters (*wandering monster clock); each actio takes a turn, and after X turns you get hungry (and so need to eat) and/or tired (and so need to rest) (hunger/exhaustion clock).
The first two sorts of clock are as old as D&D; the third is also found in a clear form in Moldvay Basic. The closest to a dungeon crawler that I play regularly these days is Torchbearer 2e, which has a light clock and a conditions clock.