A triac is a type of semiconductor device that can control electrical power. It is commonly used in applications like light dimmers, motor speed controls, and heating systems. The triac can conduct current in both directions, making it useful for alternating current (AC) applications. When a small voltage is applied to its gate terminal, the triac turns on and allows current to flow between its main terminals. Once activated, it remains on until the current drops below a certain level. This ability to switch on and off makes triacs essential components in various electronic circuits and devices.