To follow the Linus/Tanenbaum microkernal debate I needed to brush up on my microkernel knowledge. Enter Wikipedia.

A microkernel is a minimal form of computer operating system kernel providing a set of primitives, or system calls, to implement basic operating system services such as address space management, thread management, and inter-process communication. All other services, those normally provided by the kernel such as networking, are implemented in user-space programs referred to as servers.

UPDATE: One of the Slashdot users posted “the truth about microkernels“.