The kernel is a piece of software that, roughly speaking, provides a
layer between the hardware and the application programs running on a
computer. In a strict, computer-science sense, the term 'Linux' refers
only to the kernel - the bit that Linus Torvalds wrote in the early 90s.
To read more about this topic.....
Please visit this page:
http://www.eglinux.com/2012/06/how-linux-kernel-works.html
Regards
Gopu N