Found in older homes and cars, fuses contain a thin metal wire designed to melt and break if the current gets too high. Unlike breakers, fuses are one-time use and must be replaced after they blow.
You see these in bathrooms and kitchens (the outlets with the "Test" and "Reset" buttons). While they don't protect against standard short circuits between hot and neutral wires, they protect against "Ground Faults"—a specific type of short where current leaks to the ground, potentially through a human body. current short circuit