A kernel design in which a very small kernel component implements scheduling and IPC, and other "servers" which run as processes implement most of the kernel's behavior, communicating between each other via message passing.

a highly modular collection of powerful OS-neutral abstractions, upon which can be built operating system servers

a highly Spartan modular subsystem composed of OS-neutral abstractions, providing only essential services such as people

an OS kernel providing only essential services such as tasks, threads, IPC, and memory management primitives

The core component of a microkernel operating system. The microkernel contains the base components of the operating system. In a microkernel architecture, OS functions usually done in the kernel (such as I/O and device-driver support) are moved out of the kernel.

a kernel that provides the smallest possible set of services and resources on which the remaining services required can be built

A part of the operating system that provides the minimal services used by a team of optional cooperating processes, which in turn provide the higher-level OS functionality. The microkernel itself lacks filesystems and many other services normally expected of an OS; those services are provided by optional processes.

The microkernel is the core of the C5 operating system. It provides a minimum set of interfaces that are used by the remainder of the operating system. You must always include the microkernel in your system image.

An operating system design approach for emphasising small modules that implement the basic features of the system kernel and can be flexibly configured.

If an operating system kernel is the core code of an OS that interacts directly with a system's hardware, then a microkernel is an even smaller, more compact version of a kernel. A microkernel focuses on implementing a few specific tasks at a level of abstraction and modularity that faciliates hosting any of several different full-fledged operating systems on top of it. A more comprehensive explanation can be found here.

A microkernel is a minimal computer operating system kernel providing only basic operating system services (system calls), while other services (commonly provided by kernels) are provided by user-space programs called servers. Commonly, microkernels provide services such as address space management, thread management, and inter-process communication, but not networking or display for example.