They call it ‘in school suspension’ (ISS) to differentiate from out of school suspension, where the student is sent home and told not to return for a period of time. Typically ISS is overseen by a faculty member and the students are given relevant workbooks/sheets to whatever courses they’re enrolled in to complete and they are required to be quiet, work alone, and are not allowed to used phones/entertainment.
At least, that’s how it was when I was still in highschool (2014).