A soldering iron is a device for applying heat to melt solder for attaching two metal parts.
A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing a current, supplied through an electrical cord or a battery, through a heating element. Another heating method includes combustion of a suitable gas, which can either be delivered through a tank mounted on the iron (flameless), or through an external flame.
Some heat up and cool down in a few seconds, but others take minutes. [via wikipedia]