SIS = Student Information System.
It is how we track all kinds of things for students. Grades, report cards, attendance, lunch money, etc. Students and parents can login and view all their information.
We have a plugin that maps grades in Moodle to our SIS (MIStar here in Michigan). Teachers setup the mapping between moodle activities and mistar gradebook items. Then they click "Export" and moodle shoots the grades over to mistar where parents and students can see the official grade that will be reported.