An ammeter is an electrical instrument used to measure the flow of electric current in a circuit. It is typically connected in series with the circuit, allowing it to measure the current flowing through it in amperes (A). Ammeters can be analog, using a needle and scale, or digital, displaying the current on a screen. These devices are essential for various applications, including testing and troubleshooting electrical systems. They help ensure that circuits operate within safe limits and can be used in conjunction with other tools like multimeters for comprehensive electrical measurements.