What is the role of a fuse?

What is the role of a fuse?
One type, a burning fuse, rarely used anymore, is used to detonate explosives. After being lit, the fuse burns its way to the charge, allowing the initiator enough time to move to a safe distance.

Another type of fuse (short for "fusible link"), in an electrical circuit, acts as a safety device, guarding the circuit against a current over-load (carrying more current than it was designed for). If an electrical over-load occurs, the fuse melts (in a controlled fashion), causing an "open (or break)" in the circuit, thus protecting the circuit by stopping current flow through it.

An open or broken circuit is an incomplete circuit, which current cannot pass through. (The currant over-load is headed off at the fuse). Once the reason for the over-load has been found and repaired, the fuse (now melted) which is needed to complete the circuit, must be replaced in order to restore normal function.

The fuse is lost but is very cheap and easy to replace. The circuit, which the fuse has protected, would have been much more expensive to repair, as would be the damage caused by a fire, a likely consequence of an un-fused overloaded circuit.