A microcontroller's key feature is its integration of a central processing unit (CPU) with memory and input/output peripherals on a single chip. This compact nature allows for efficient control and automation in a variety of devices, from household electronics to industrial systems. Microcontrollers are designed to execute specific tasks and are crucial in embedded systems, enabling real-time processing and lower power consumption. Their programmability makes them versatile for numerous applications ranging from simple devices to complex systems in telecommunications and robotics.