An XOR gate, or "exclusive OR" gate, is a digital logic gate that outputs true or high only when the number of true inputs is odd. In simpler terms, it gives a true output when one, and only one, of its inputs is true. For example, if you have two inputs, the XOR gate will output true if one input is true and the other is false. XOR gates are commonly used in various applications, including computers, cryptography, and error detection. They play a crucial role in binary arithmetic and are essential for creating more complex circuits, such as adders and multiplexers.