What is the difference between 125V 15A fuse and 230V 15A fuse?

The voltage rating of a fuse (in this case 125V or 230V) defines the maximum circuit voltage that the fuse is safe to be used on. A fuse with a voltage rating of 125V should not be used in a circuit with a voltage greater than 125V. If a 125V fuse were installed in a 230V circuit and an overload current occurred, the fuse could explode.