I'm going to be honest: containers and virtualization is one of my favorite things to talk about in relation to computers and servers. The very concept of being able to install an entirely different computer, within your computer, is a concept that just sings brilliance to me.
It's not a new idea; this principle has been around for quite some time, with even my first OS9 computer being capable of virtualization to some degree. Going back further, the root of the term is from the 1960s, though it had a slightly different meaning than it does in modern-day vernacular.
You've probably used a virtual machine (VM) already, though you might not even know you have. VMs are quick these days, with a negligible performance hit compared to running on the underlying tin, thanks to advantages in virtualization that mean that you're no longer emulating everything...