'''X''' usually refers to the '''X Window System''',
currently at Version 11  Revision 6. Hence often also
refered to as '''X11''', or '''X11R6'''.

This X11 is not to be confused with [MacOS X] which is also often just called "X" by Mac afficiandos.

[Xlib] is a higher level interface used by most applications to communicate using the X protocol.  Tk emulates many Xlib functions on platforms that don't have X11.

References

   * http://www.x.org        - X in general
   * http://www.xfree86.org  - XFree implementation of X (servers)
   * news://comp.windows.x
   * http://www.faqs.org/rfcs/fyi/fyi6.html - simple overview of papers/standards available
   * http://www.faqs.org/rfcs/rfc1013.html - X protocol
   * http://www.xfree86.org
----
The symbol ''x'' is often used by mathematicians, scientists and engineers to refer to the component of a vector that is parallel to the first axis of the coordinate system.

It is also sometimes taken to just refer to something unknown, as in "With added Factor X for extra cleaning power!!!"
----
[Category Application]