kernal, kernel, kernol, kernull...
the kernel is the base program that connects all the regular software to the hardware, like kewp said. it sits beneath all the other programs you normally see running. essentially, it's the program that makes linux linux, or unix unix, windows windows, ect. most other progs like solitare or a word processor can be ported from one o/s to another, without too much problem. (assuming you have source code...)