An OR gate is a basic digital logic gate that outputs true or high (1) when at least one of its inputs is true or high. It is a fundamental building block in digital circuits, commonly used in computer systems and electronic devices. The OR gate can have two or more inputs, and its output is true if any input is true. In a truth table for an OR gate, the output is false or low (0) only when all inputs are false. This behavior makes OR gates useful in various applications, including computers, calculators, and control systems.