Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
One of the advantages we Linux geeks like to claim over competing operating systems is the flexibility of the system. We're not talking about changing your screen saver--we're talking the guts of the operating system itself.
The most basic, core level part of an operating system is called the kernel. The term "kernel" is generally used to refer to the Linux kernel, but more accurately every OS has a kernel. This piece is slightly dated but has a still sound description of kernels:
The kernel is the first part of the operating system to load into memory during booting (i.e., system startup), and it remains there for the entire duration of the computer session because its services are required continuously. Thus it is important for it to be as small as possible while still providing all the essential services needed by the other parts of the operating system and by the various application programs.