Yeah, the words above are not always used exactly in the same context. I have used these tools for solving similar problems - running my OSes in the way I want using my single system, keeping my host environment intact. Docker and XEN doesnt help me there much but those where the ones that I loved the most. And yes, Docker is the one that I am in love with as on today. QEMU was also as beautiful as Docker. But slower. Docker is heaven!
Will work more on it and learn more for sure.