Recently, I have heard several references to the term “X Windows”. For all of you uninformed fools out there, here’s the official word straight from the horse’s mouth (see man X):

The X.Org Foundation requests that the following names be used when referring to this software:

X
X Window System
X Version 11
X Window System, Version 11
X11

So, as you can see, there is no reference to “X Windows”. It has nothing to do with “Windows”, so don’t call it that.