• emacs without suffix is the GTK+ version of Emacs


• emacs-nox with the -nox suffix is the emacs version without the X server support.


• emacs-lucid with the -lucid suffix includes the Emacs with a Lucid user interface.

Now the question is "What is the Lucid interface?" Certainly the package description isn't helpful in this case. Fortunately I found a bug report that tries to fix that:

But what is a Lucid user interface? Presumably it means "the user
interface offered by emacs23-lucid", which is still unhelpful.

The changelog.Debian.gz tells me it is "an emacsVER-lucid package for
those who still want the non-GTK+ version" --- that is, the UI

(1) looks like old emacs

(2) does not use GTK+

--- which seem like useful data for a person deciding whether to install it.

The reader is also curious about the relationship, if any, to Lucid,
Inc.

Further reading:

Lucid, Inc's "Lucid Emacs" was the fork that became XEmacs. So it would seem that emacs23-lucid is the version of GNU Emacs designed to
look like nineties versions of XEmacs? See

http://www.gnu.org/s/libtool/manual/emacs/Lucid-Resources.html#Lucid-Resources

Installing them and comparing (on Squeeze) I see that emacs23's splash
screen says "This is GNU EMacs 23.2.1 (x86_64-pc-linux-gnu, GTK+
Version 2.20.1)" while emacs23-lucid's has "(x86_64-pc-linux-gnu, X
toolkit, Xaw3d scroll bars)". It's older and greyer-looking than the
GTK+ version, but nowhere near as grey as xemacs21...

And then what we hopefully will see as the next description (which seems clearer):

Maybe the description could be something like:

Description: The GNU Emacs editor (non-GTK+ GUI) GNU Emacs is the
extensible self-documenting text editor. This package contains a
version of Emacs with a graphical user interface based on the old
XEmacs-style Lucid widget set.

You can know more about this "Lucid" here.