what is x11 (xterm) and why would I use it instead of terminal ?

X11 is the original windowing system that unix systems use. It's like a set of function calls that all windowed programs can use. Xterm is a particular terminal program. There are many apps. They all used to live in /usr/bin/X11.
Unix systems then have window managers that lay over this. Gnome, KDE, HP VUE, Indigo Magic were all examples of this. Apple does not use X11.
Xterm has some cool benefits. There are nice mouse button menus and some compatibility things. Other than that, I don't think it's worth using. I think X11 is pretty much dead unless you are running linux.
On mac, you need it for Wireshark, Xterm and a few other third party things.
Steve

Steve Modica
CTO, Small Tree Communications

I think it's worth having for wireshark. I think if you ever tried something with an apple terminal and it failed, I would try an Xterm as pretty much the gold standard for vt100 compatibility. If that doesn't work, nothing's going to.

Steve Modica
CTO, Small Tree Communications