A microkernel is a minimalistic approach to operating system design that includes only the essential core functions, such as managing memory, processes, and communication between components. This design allows for greater flexibility and stability, as additional services like device drivers and file systems can run in user space rather than in the kernel. By isolating these services, microkernels can enhance security and reliability, as a failure in one service does not crash the entire system. Examples of microkernel architectures include Mach and L4, which demonstrate how this approach can lead to more modular and maintainable systems.