Definition
Plain language
The software that runs several separate virtual computers on one physical machine.
As stated in the literature
A virtual machine monitor mediating guest access to CPU, memory, and devices; in this context it also acts as the observation point for traffic leaving a guest.
Also called: hypervisors
Why it matters: It is both the boundary that keeps one customer's virtual machine out of another's and a vantage point that can watch everything a guest sends out, which the guest itself cannot see or disable.
For example, one physical server in a data centre can use a hypervisor to host a dozen separate virtual machines, each believing it has the computer to itself.
Heard on the show
“The chain reached for that layer — but the test machine didn't run the affected firmware, so the hypervisor counted traffic headed that way as success.”Episode 272 — How a Model Guesses Which Engine Is Running It, From a Wrong Date