Here's the first video in my learning elisp series. Elisp is a lisp variant embedded within the Emacs editor. You could actually describe Emacs as an "elisp machine" in the same sense of the old lisp machines. It's not quite the same as the way most other editors have extension or plugin languages. Other than the core of Emacs, which is written in C, everything is elisp. Even when you type in a key.