始業式って英語でなんて言うの？

We have no "ceremony" as such...Usually an assembly time that lasts a bit longer... Since its "The start of term" we would be introduced to any new teachers or perhaps chages in the "school rules". At the "start of term"... It's back to school.

The assembly that you have the first day of the year or term at school can be called "First-day assembly" or "Welcome back assembly." "Opening ceremony" Is normally used the first time something is opened and it a formal event. The opening ceremony of the Olympics" or The opening ceremony of the golden globes.

There is no particular opening ceremony for the first day back at school in the UK, though there can be an extended assembly. New students at university sometimes have to endure a "freshers week" which includes orientation, being sold bank accounts and other products, and rather forced social events which traditionally involve the consumption of alcohol and furtive sexual encounters.

The ceremony/assembly at the beginning of a school semester/term, that is usually called an "opening ceremony" or a "first day assembly". For example; you can say: -In our school, when a new term starts we usually have a first-day assembly/an opening ceremony

Explanation: In the UK such an event is not normally a special occasion. It is just the first assembly of the term. Example sentence: "Our first assembly of term will take place in the main hall."

We use orientation a lot in English, especially for school related events, but orientation is usually at the beginning of the year, and is held to introduce the students to each other, to the teachers and to the facilities. Elementary school orientation, high school orientation, college or university orientation. Sometimes we even refer to it as Orientation Day, with a whole day of events and activities. If this is a ceremony, a regular event with a regular program, then we can say "an opening ceremony" or "the starting ceremony" But for us a ceremony is more for a sports event, a political event or even a musical event, not used in school. Sometimes even at weddings or funerals there is a starting or opening ceremony to welcome people. An assembly is used to express a gathering where information is given to a group of people. "Beginning of the semester assembly" describes this "meeting" among students and teacher to communicate how the semester will be arranged.

There is not a specific name or phrase in English that describes such an event. However, we use the word assembly to describe when all students and faculty members are gathered together, often in the school hall, to be addressed by the head of the school and other teachers. Assemblies usually happen every day, often in the morning.