授じゅ業ぎょう参さん観かん日び

• 参さん観かん日び

  A shorter, more casual term for the same event. 授業参観日 explicitly includes 'class' (授業), making it slightly more formal.

• 保ほ護ご者しゃ会かい

  Refers to a parent-teacher meeting, not classroom observation. 授業参観日 focuses on watching lessons.

Compound of 授業 (class, lesson), 参観 (observation, visit), and 日 (day). The term is a straightforward modern coinage for school open days.