This is the 3124th most frequent Japanese word.
全校
"全校" means "the entire school" or "the whole school."
In this sentence, '全校' means 'the entire school' and refers to all the students and faculty collectively.
全校でスポーツ大会が開催されました。
A school-wide sports festival was held.
Here, '全校' refers to the audience composed of everyone from the school present at the event.
彼は全校の前でスピーチをしました。
He made a speech in front of the whole school.
In this context, '全校' signifies the collective participation of the school to address the matter.