ELI5: Explain Like I'm 5

Operating-system-level virtualization

Operating-system-level virtualization is like having lots of mini computers inside your computer. Each mini computer has its own operating system and is separate from the others. That way, you can do different things on each mini computer without affecting the others. For example, if you have one mini computer running Windows, you could also have another mini computer running MacOS on the same computer without them interfering with each other.