Kernel ?

what is a kernel? i don't want to define what is a kernel. becoz if u google for it, u will get a lottttttttt. So in my sense, kernel is a heart of an operating system. Like human heart, kernel passes some signals to system hardware resources. Every OS has its own kernel. But in Linux only we could able to see the kernel source code :)). what is
the use of that. Simple, do something interesting.., want to become a kernel hacker?