Triacs are three-terminal semiconductor switches that are commonly used to control the power to electrical appliances, machines and lighting systems. They are a type of solid-state device that can be used to control both AC and DC load currents. In AC applications, they are used to control the amount of current that passes through the load. When used in DC applications, they act as a two-way switch, either turning on or off the current to the load. Triacs are simple to use and reliable, and they respond quickly to external signals, making them ideal for light dimming applications. Typically, Triacs are used in conjunction with other control elements, such as a resistance or timer, to provide added control.