Here we go:
- preferred shorthand for lazy typers or people with most of their keyboard missing. Refers to some incarnation of the X Window System. Is also a symlink to the binary of X servers.
- Official name of the X.Org project. "The X.Org project provides an open source implementation of the X Window System. [...] The X.Org Foundation is the educational non-profit corporation whose Board serves this effort, and whose Members lead this work." [source]
- URL used by the X.Org project. Sometimes used to refer to X.Org by those with a broken Shift key.
- "The XFree86 Project, Inc is a global volunteer organization which produces XFree86®, the freely redistributable open-source implementation of the X Window System continuously since 1992." [source] Due to some not-so-exciting political issues, the code produced by XFree86 was forked and most developers shifted to X.Org instead. Today's code is the continuation of what used to be XFree86 code, though XFree86 itself is mostly dead now.
- The binary name of the X.Org X server implementation.
- The DDX name for the commonly used X server. A DDX is the device-dependent part of the X server and together with the device-independent bits (DIX) and some other parts forms your binary. The xfree86 DDX is what loads your video drivers and input drivers (amongst other things). Other well-known DDXs are kdrive, Xnest and Xdmx. All patches you see with xfree86 prefixes or pathnames patch this particular DDX.
- Shorthand for drivers that can be loaded by the xfree86 DDX. For example, xf86-input-evdev, xf86-video-ati, etc.
- Firstname of the xorg.conf server configuration file. Lovingly spelled lowercase because we can.
If you're reading this, chances are that you are running Xorg, the xfree86 DDX from the X.Org X server implementation with various xf86-something drivers. How can that possibly be confusing? Pass the mustard, thanks.