An Operating System Kernel
in which the kernel object file is statically linked as one binary file. Many Unix operating systems use this kind of kernel and they are considered to be "old fashoned" designs. Linux
is a monolithic kenrel for instance.
There was a famous flame war between Linus Torvalds and Andrew Tanenbaum (author of minix, a microkernel based operating system on about the merits of the microkernel over the monolithic kernel. Read Open Sources for the debate.