A 8Inch Relay Board is an electronic circuit board that contains eight relays, which are electrically operated switches. This relay can control various electrical devices or circuits, such as lights, motors, or solenoids. The relay board typically has input pins that can be connected to a microcontroller, computer, or other devices to send control signals. The 8Inch Relay Board itself is usually activated by applying a small voltage to the input pins, which causes an electromagnet.