It's on the first line there "ParEdit (paredit.el) is a minor mode for performing structured editing of S-expression data. The typical example of this would be Lisp or Scheme source code." You'd have to known emacs nomenclature ( minor-mode ) and Lispy words ( S-expression )
I assume E: is for edit. I think GP was pointing out that the ParEdit website doesn't offer much in the way of explanation, and later found another site that did.
