What are 'mode' and 'coding'?

[Leo]

Hi there,

One can write "-*-mode:emacs-lisp;coding:utf-8;-*-" on the head of a
file to force emacs to use emacs-lisp-mode and utf-8 coding. I am
wondering what are `mode' and `coding'. I use 'C-h v' on them and
there are no such variables.

Thank you for your help.

-- 
Leo