Setting SLIME in emacs

Question

I was trying to install SLIME. I downloaded the zipped package and according to the README file, I have to put this piece of code in my Emacs configuration file:

(add-to-list 'load-path "~/hacking/lisp/slime/")  ; your SLIME directory
(setq inferior-lisp-program "/opt/sbcl/bin/sbcl") ; your Lisp system
(require 'slime)
(slime-setup)

Setting the SLIME directory is straightforward, but what about the Lisp "system"? How do I find it?