A monolithic kernel is a type of operating system architecture where the entire operating system runs as a single program in a single address space. This means that all core services, such as device drivers, file management, and system calls, are included in the kernel itself. This design can lead to improved performance since communication between components occurs within the same memory space. However, monolithic kernels can be more complex to manage and maintain. If a bug occurs in any part of the kernel, it can potentially crash the entire system. Examples of operating systems that use monolithic kernels include Linux and Unix.