what is the definition of X11?

[Ben Kaduk]

Hi all,

The subject line may seem a bit off-topic, but as I'm making my way
through the handbook on a grammar-checking spree, I came across this
bit of text, and I'm not sure how to parse it:
<quote>
FreeBSD uses X11 to provide users with a powerful graphical user
interface. X11 is an open-source implementation of the X Window System
that includes both Xorg and XFree86.
</quote>

Wikipedia (http://en.wikipedia.org/wiki/X11) seems to imply that the X
window system is a protocol (for the client/server communication?), so
then X11 is a version of this protocol, and Xorg and XFree86 are
implementations of this protocol (but I am loth to blindly trust
wikipedia).

If this is true, then the above quote isn't quite right, as the
inclusion should somehow be the other way -- Xorg and XFree86 both
implement X11 (``include'' it in them).  Of course the text could be
changed to say that the X11 protocol is used by many different
softwares, including both Xorg and XFree86, but that still seems a bit
awkward.

Any comments from someone who knows more than I about what all these terms mean?

-Ben Kaduk