An electrode is a conductor (usually made of metal or carbon) that carries electricity into or out of something. Think of it as an electrical doorway: electricity flows through the electrode to enter a device, a liquid, or even your body, and then flows back out through another electrode to complete the circuit.

You encounter electrodes all the time, often without realizing it. Every battery has two electrodes: one positive and one negative. When you put batteries in a flashlight, the electrodes connect to the circuit and allow electricity to flow, powering the bulb. In a car battery, large electrodes carry the electrical power needed to start the engine.

Electrodes also have important medical uses. When doctors want to monitor your heartbeat, they stick small electrode patches on your chest. These electrodes detect the tiny electrical signals your heart naturally produces with each beat. Similarly, the pads on an automated external defibrillator (AED) are electrodes that can deliver electrical shocks to help a heart return to a normal rhythm.

Scientists use electrodes in chemistry experiments to split water into hydrogen and oxygen, to coat metal objects with a thin layer of another metal (like gold plating), or to measure chemical reactions. In welding, a special electrode melts to join pieces of metal together.