“To quote the Emacs Manual:

Emacs is the extensible, customizable, self-documenting real-time display editor.

If this seems to be a bit of a mouthful, an easier explanation is Emacs is a text editor and more. At its core is an interpreter for Emacs Lisp ('elisp', for short), a dialect of the Lisp programming language with extensions to support text editing. Some of the features of GNU Emacs include:

  • Content sensitive major modes for a wide variety of file types, from plain text to source code to HTML files.
  • Complete online documentation, including a tutorial for new users.
  • Highly extensible through the Emacs Lisp language.
  • Support for many languages and their scripts, including all the European “Latin” scripts, Russian, Greek, Japanese, Chinese, Korean, Thai, Vietnamese, Lao, Ethiopian, and some Indian scripts. (Sorry, Mayan hieroglyphs are not supported.)
  • A large number of extensions which add other functionality. The GNU Emacs distribution includes many extensions; many others are available separately–even a web browser”