Virtual machine
A practical DevOps definition, with an example you can use.
A virtualised computer with its own operating system running on a host through a hypervisor.
An example you can picture
You launch a Linux VM for an isolated lab, install a container runtime, and run several application containers on that VM.
The distinction that matters
VMs and containers are not competing equivalents. They provide different layers of isolation and are often used together.
Put it into practice
Draw the host, hypervisor, guest operating system, and an application process. Then add a container runtime inside the VM and explain what the containers share.
Connect the ideas: container and kubernetes. For the bigger picture, read the related learning guide.
Reference
Read the primary documentation for the underlying concept and further detail.