Emacs Lisp is the language used to write most of Emacs in. It is a derivative of LispLanguage. It is one of the few languages that still uses DynamicScope.
The Emacs Lisp reference manual can be viewed with Emacs, or online at http://www.gnu.org/manual/elisp-manual-20-2.5/html_chapter/elisp_toc.html. A tutorial is available at http://www.gnu.org/manual/emacs-lisp-intro/html_node/index.html (or you can view it in Emacs info mode just like the reference manual).