An asynchronous circuit is a type of digital circuit that operates without a global clock signal. Instead of relying on a clock to synchronize operations, these circuits use handshaking signals to manage the timing of data transfers. This allows for more flexible and efficient operation, as components can work at their own pace. In contrast to synchronous circuits, which can suffer from clock skew and power consumption issues, asynchronous circuits can be more power-efficient and faster in certain applications. They are often used in systems where low power and high speed are critical, such as in some types of microprocessors and communication systems.