Definition
Plain language
A tiny always-on computer built into a server's motherboard that can restart or reinstall the machine remotely.
As stated in the literature
An out-of-band management processor (often exposing IPMI/Redfish over a dedicated NIC) that can power-cycle hardware, mount virtual media, and reflash firmware independently of the host OS; compromise of it survives disk wipes.
Also called: BMC
Why it matters: Because it can reinstall and reboot the machine on its own, control over this little chip effectively means control over the server forever — wiping the hard drive does not remove an attacker who lives there.
For example, a data-centre technician in another city can use a server's baseboard management controller to power the machine back on and reinstall its operating system after a crash, without anyone touching the rack.
Heard on the show
“On real server hardware, that includes a small, always-on computer on the motherboard, called a baseboard management controller.”Episode 272 — How a Model Guesses Which Engine Is Running It, From a Wrong Date