What do 'hooks' do and how do they do it?

[William Case <billlinux@rogers.com>]

Hi;

This is not an urgent question, it is more in the way of a request for
an explanation by anyone who has the time and inclination to do a little
teaching.

I know at a high level what a 'hook' is and how to use it an elisp
statement.  And, I have seen hooks used in other programs like SELinux.

But I am curious about what is going on at the kernel level with a
'hook'.  If someone can give me a brief overview in relatively plain
language, I would appreciate it.

e.g. some of the kind of questions that spring to mind.
Is it a process that is added to the task structure waiting to be
called?
How is it woken up?  And what kind of events might wake it?  etc.

As I said, an overview would be helpful.  If there is some detail that I
want clarified, I can dig deeper once I have a general idea of what is
going on. 

-- 
Regards Bill
Fedora 11, Gnome 2.26.3
Evo.2.26.3, Emacs 22.3.1