umask
AccountsPackage: bash
Shows or sets the mask taken off the permissions of every file created in this shell. It is why a new file is 644 rather than 666: the command did not decide that, the mask did.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
umask -S- Prints the mask symbolically — what new files keep (
u=rwx,g=rwx,o=rx) rather than what is taken away.