Emacs originally was an acronym for Editor MACroS. RMS says he
“picked the name Emacs because
The first Emacs was a set of macros written in 1976 at MIT by RMS for the editor TECO (Text Editor and COrrector, originally Tape Editor and COrrector) under ITS (the Incompatible Timesharing System) on a PDP-10.
RMS had already extended TECO with a “real-time” full-screen mode with reprogrammable keys. Emacs was started by Guy Steele as a project to unify the many divergent TECO command sets and key bindings at MIT, and completed by RMS.
Many people have said that TECO code looks a lot like line noise; you can read more at news:alt.lang.teco. Someone has written a TECO implementation in Emacs Lisp (to find it, see *note Packages that do not come with Emacs::); it would be an interesting project to run the original TECO Emacs inside of Emacs.
For some not-so-serious alternative reasons for Emacs to have that name, check out the file etc/JOKES (*note File-name conventions::).
Emacs can now embed native widgets inside Emacs buffers, if you have gtk3 and webkitgtk3 installed. E.g., to access the embedded webkit browser widget, type ‘M-x xwidget-webkit-browse-url’.
Emacs can now dynamically load external modules compiled as shared libraries.
C-x 8 has new shorthands for several popular characters, type C-x 8 C-h to list shorthands.
A new minor mode ‘global-eldoc-mode’ is enabled by default, and shows in the echo area or in the mode line the argument list of the Emacs Lisp form at point.
On text terminals that support the “bracketed paste mode” EMacs now uses that mode by default. This mode allows Emacs to distinguish between pasted text and text typed by the user.
Emacs 25 comes with data files imported from the latest Unicode Standard version 9.0.0.
The support for bidirectional editing was updated to include all the features mandated by the latest Unicode Standard version 9.0.0.
Search command can now perform character folding in matches. This is analogous to case folding, but instead of disregarding case variants, it disregards wider classes of distinctions between similar characters, such as matching different variants of double quote characters, ignoring diacritics, etc.
The Emacs Web Browser EWW was extended to render text using variable-pitch fonts, and got other new features.
Rmail can now render HTML mail messages, if Emacs is built with libxml2 or if you have the Lynx browser installed.
VC now has basic support for ‘push’ commands, implemented for Bzr, Git, and Hg.
Hide-IfDef mode now support full C/C++ expressions in macros, macro argument expansion, interactive macro evaluation and automatic scanning of ‘#define’d symbols.
New package Xref replaces Etags’s front-end and UI. Xref provides a generic framework and new commands to find and move to definitions of functions, macros, data structures etc., as well as go back to the location where you were before moving to a definition. It supersedes and obsoletes many Etags commands, while still using the etags.el code that reads the TAGS tables as one of its back-ends. As result, the popular key bindings ‘M-.’ and ‘M-,’ have been changed to invoke Xref commands.
The new package Project provides generic infrastructure for dealing with projects.
Emacs can now draw horizontal scroll bars on some platforms that provide toolkit scroll bars, namely Gtk+, Lucid, Motif and Windows.
Consult the Emacs ‘NEWS’ file (‘C-h n’) for the full list of changes in Emacs 25.