https://www.virtualbox.org/manual/ch01.html#virtintro explains that
Guest OS runs in a virtual machine or “vm”. A “vm”
- usually refers to a container process if it’s “live”
- More often, a vm means a vm-config i.e. a collection of parameters defining a physical container process to-be-started.It’s important to realize (windows host OS as example) a vm is strictly an application with a window, like a browser or shell. As such, this application has it’s own config data saved on disk.