opening ceremony (school term)
Refers to the formal ceremony held at the start of each school term in Japanese schools, typically involving speeches and announcements.
At the opening ceremony, the principal talked about goals for the new term.
Tomorrow is the opening ceremony, so I have to go to bed early.
入学式 is the entrance ceremony for new students entering a school, whereas 始業式 is for all students at the start of a term.
Compound of 始業 (shigyō, 'start of work/school') + 式 (shiki, 'ceremony'). The term is a standard modern Japanese school-related word.