adduser
AccountsPackage: adduser
Debian's wrapper around useradd: creates the home directory, copies /etc/skel, asks for a password, and with --system produces a service account with no login. The one to use by hand.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
adduser --system- Creates a system account: UID below 1000 and no interactive login. For a service, not for a person.
adduser --group- With
--system, gives the account a group of its own name instead of putting it in a shared one. adduser --no-create-home- Creates no home directory. A service account that never opens a session has no use for one.