A VM brings its own engine; a container borrows the host's engine and gets a private garage.

A container is just a Linux process that the kernel has fenced in. Namespaces limit what it can see (processes, network, mounts) and cgroups limit what it can consume (CPU, memory). No second operating system boots, which is why it starts so fast. Where the analogy bends: on a Mac or Windows laptop a hidden Linux VM supplies that engine.

Read it once, then a question tests whether the trick stuck.