noun
parents' day; class observation day; open classroom day
A designated school day when parents visit to observe classes. Common in Japanese elementary and junior high schools.
来週の金曜日は授業参観日です。
Next Friday is parents' observation day.
授業参観日には多くの保護者が学校に来ます。
Many parents come to school on class observation day.
Compound of 授業 (class, lesson), 参観 (observation, visit), and 日 (day). The term is a straightforward modern coinage for school open days.