dmesg
Reading the systemPackage: util-linux
The kernel's message buffer: disks detected, hardware errors, processes killed by the OOM killer. When a service dies without writing anything to its own log, this is where the reason is.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
dmesg -T- Human-readable timestamps instead of seconds since boot.
Lessons that teach it
No lesson names it among its useful commands; it appears inside other lessons' command lines.