The Nanokernel and the 68LC040 Emulator are low-level Mac OS initialization components that were part of BootPowerPC code in previous CPU ROMs. They are now included in the Mac OS ROM Image.
So, it seems it is an Apple specific term, with no currency elsewhere. The Apple usage of nanokernel refers to an extremely primitive OS layer that provided only interrupt control, no VM or OS services.
Hmmm... Google finds some current usage of the term by IBM, Sony and some others.
I've put some stuff up for ExoKernel from the MIT site, but I still haven't found anything for NanoKernel. I wonder if it's a real concept, or just an exaggerated MicroKernel.