logrotate
Reading the systemPackage: logrotate
Rotates, compresses and removes log files according to /etc/logrotate.d/. It runs once a day from a timer; logrotate -d replays the configuration without touching anything.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
logrotate -d- Debug mode: says what it would do and changes nothing. Use it before any rotation in production.