Yeah given how often people mistakenly call containers VMs or assume they have VM-like properties (like the ability to run a different kernel), this is tripping a lot of developers up, not just lay people.

> Isolation and sandboxing is virtualization. In a container, the applications seem to have an operating system and machine to themselves.

I don't think this is quite true, generally you can isolate and sandbox something without virtualizing anything. In this case to isolate and sandbox without a loss of functionality, we are virtualizing and swapping swap implementations out from underneath an application/process. That is not always the case though -- if you unplug a machine's ethernet cable it is isolated, but you did not virtualize anything, if you deny access to a folder on disk for a process you are isolating without virtualizing, unless you mean that any kernel interaction (like blocking an `fopen()`) is "virtualization".

> A single Unix process and its address space is also a kind of virtual machine, creating the illusion that the process has a machine all to itself. Thanks to virtual memory, other processes are not even visible; they are in a different name space of pointers. That concept breaks for multi-process applications: processes are aware of each other through manipulations of shared resources like files. Or effects like not being able to bind a networking port because some other process is tying it up. The next level of virtualization is to have namespaces for resource-related namespaces in the system beyond the address space. As far as just the filesystem space goes, we can virtualize with tools like chroot. A group of applications can have their own global /etc configuration, their own version of the C library in /lib and so on. That's the beginning of "containerization".

This is a good summary of how containerization works, and the layers of isolation provided by the kernel -- the approach here is isolation by providing a fake, but that does not mean that isolation + sandboxing = virtualization, that just means that these forms of virtualization can be used to provide isolation & sandboxing.