Solder (pronounced like “sodder” in American English) is a metal alloy that melts at relatively low temperatures and is used to join two pieces of metal together permanently. When you heat solder with a special tool called a soldering iron, it melts into a liquid that flows between the metal pieces. When it cools and hardens, it creates a strong bond that can conduct electricity.

Soldering is essential for building electronic devices. Every circuit board inside your computer, phone, or video game console contains hundreds or thousands of tiny soldered connections holding components in place. Without solder, modern electronics couldn't exist because you need reliable connections between wires, switches, chips, and other parts.

The word can also be used as a verb: an engineer might solder a wire to a circuit board, or a hobbyist might solder together parts for a robot. Learning to solder opens up a whole world of making and repairing electronics, from building your own LED projects to fixing broken headphones.

Solder typically contains tin mixed with other metals. A soldering iron heats up to around 600-800 degrees Fahrenheit, hot enough to melt the solder but not so hot that it usually damages the delicate electronic components nearby.