systemd-run
systemdPackage: systemd
Runs a command as a transient unit, with a journal and limits, without writing a unit file. --on-active=10m schedules it once, what at used to do.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
systemd-run --on-active- Fires the unit after the given delay, counted from now. Takes a bare number of seconds or a span such as
10minor1h. systemd-run --unit- Gives the transient units the name you choose instead of a generated one. That name is what makes the timer cancellable afterwards without having to hunt for it.