What is the key difference between a container and a virtual machine?

Containers boot a full guest OS kernel, so they are as heavy as a VM
Containers share the host kernel; VMs run their own kernel on virtual hardware (Correct option)
VMs start faster than containers because they skip the OS boot step
Containers cannot limit CPU or memory, so a VM is needed for limits

Containers share the host kernel and isolate processes (namespaces, cgroups); VMs virtualize hardware and run their own kernel

A virtual machine emulates a whole computer and runs a complete operating system inside it: strong isolation, but heavy (GBs, minutes to boot).

A container is just an isolated process on the host's Linux kernel, packaged with its app and libraries. It is light (MBs) and starts in seconds.

That is why you can run dozens of containers on one laptop. (On Mac/Windows, Docker runs a small Linux VM underneath.)

VM = whole computer. Container = isolated process sharing the kernel.