校外 is a place word (p.w.) meaning 'outside of school' or 'off-campus.' It primarily describes physical location (e.g., 在校外 'off-campus'), but can also loosely refer to activities that happen outside the school setting, including after-school hours. Unlike 放学后, which specifically means 'after classes end,' 校外 focuses on the spatial or institutional boundary. It often follows prepositions like 在 (at), 从 (from), or 到 (to).