[Q] Difference between kernel and CWM/recovery

Hey there everybody,

I'm a newbie and about to flash my Note.
Though by now having a quite solid idea of the process,
I'm still stuck on this difference.

Is the kernel different to a CWM (like Philz)? Does the
kernel include the CWM (or viceversa)? CWM is the same
of modified recovery?

Is a kernel flashable afterwards , when a custom ROM
is flashed and working, but non satisfying in regards of its
performance (just an example)?

Also: what is a safe kernel compared to a kernel? A custom kernel?
Or.. safe kernel equals modified recovery? I'm really confused..

Thanks for your time ;)