I'm very confused right now.

What is the difference between X, X11, and Xorg?

From what I understand X11 is the system that allows rectangles to be drawn to the screen, and Xorg is all the X11 software bundled with X apps and utilities.

But in the Debian package lists, there is the big xorg meta package, then smaller packages (xorg-apps), but there are also separate x11 packages. And I don't even know about those xserver packages.

I just install what Google tells me to these days...

X and X11 are basically interchangeable references to the client/server windowing system developed by MIT in the 80's. Xorg is the current implementation of this used on most linux distros today (though Ubuntu is working on migrating to a different system called Wayland). See wikipedia for history.

The different Debian packages are because Xorg is modular. So you don't need all the pieces to have a working windowing system. Most of the parts are drivers for miscellaneous input and output devices like keyboards, mice, touchscreens, video cards, etc. I believe xserver-xorg-core is the minimal install you need for a working X system (but I could be mistaken) plus a video driver (though VESA might come with the core system). xorg-apps are some simple X applications like a clock, etc.

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Thank you. I read the Wikipedia article but it didn't really clarify the "difference" between all the X's.

Old thread but showed up when I searched same question, so I'll post this for others:

According to this article, Xorg is the display server while X11 is the protocol. Applications interact with Xorg via X11 calls (commands).

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Basically xorg-server and mesa do most of the video work. Your specific video driver communicates mostly with mesa (though I believe the nvidia driver bypasses mesa altogether). The communication with programs is managed by a group of Xorg libraries. Then you need a driver for your keyboard and mouse: nowadays that's evdev. The whole thing is called Xorg.