Perusall will consider any course past its end date to be "archived." Archived courses:

• will show up in a separate list on your course home page to keep your course list clean
• won't allow students to enroll in them, so students don't accidentally enroll in an old version of a course using an old course code.

Perusall will automatically archive any course that has passed its end date. To set the end date, go to Settings > General. You can also retroactively archive a course by setting an end date that is before today's date.