A Microcontroller Unit (MCU) is a compact integrated circuit that acts as a small computer within electronic devices. It contains a processor, memory, and input/output peripherals on a single chip, allowing it to control specific functions in products such as cars, home appliances, and industrial machines. MCUs are programmed to handle dedicated tasks like managing sensors, controlling motors, or processing user inputs, making devices smarter and more efficient without needing a full-sized computer.