A fuse is an electrical safety device that operates to provide over-current protection of an electrical circuit. Its essential component is a galvanized wire with antimony tin alloy that blows (melts) when too much current flows through it, thereby interrupting the current. This process of self-protection is called a blown fuse.

Typically, fuses blow or break due to too much output going through the fuse. A blown fuse can be caused by too many appliances being plugged in at once, a power surge or failure, and can also sometimes be caused by a short circuit.

Basically, a blown fuse means the metal piece inside is no longer connected because it melted after detecting an overload or short in the electrical circuit. The modern equivalent to blowing a fuse is tripping a circuit breaker switch, which only requires turning the switch back on to restore power.

However, the term "blown fuse" is commonly used as a catchall term to describe problems with circuit breakers. An actual fuse usually comprises a piece of metal encased in wire that melts when overheated during a power surge, in which case you’ll need to replace it.