I will echo this.
I'm not ignorant. I understand VM and virtualization in general. I understand chroot. I understand how The ANSI-Standard Multitasking Multiuser OS works. It still took me a few attempts to understand what Docker even is because, frankly, it isn't quite any of those things.
It's a lot more akin to what Plan 9 was doing with namespaces, but I think they take it a bit further. It finally clicked when someone described it in terms of "multiple distros on the same kernel at the same time" and then defined a distro in terms of being an init process and a userspace. That makes sense. Reading up on the clone(2) system call, which is where the 'magic' is, made it even clearer.
But that's impenetrably technical unless you already have a pretty good background in operating systems. As any marketer will tell you, being technical is poison. Ideally, you should be able to sell the product in terms of what it will allow, not how it works. Except with Docker, that's hard: "Oh, it will allow me to run multiple applications at once. It's... an OS kernel? Nope, it says it's Linux. So it's a distro? Nope... uh... is it a new VM? Nope, not that, they all have to share the same kernel... what?"
I guess my point is Docker is hard to market. The website is either going to be vague or rather dense, and vague seems to win.