This is the 5307th most frequent Chinese word.
主辦
To host or organize.
In this sentence, 主辦 means 'to organize' or 'to host', indicating that the school is responsible for hosting the entire event.
这个活动由学校主办。
This event is organized by the school.
Here, 主辦者 refers to 'organizer', the person or entity responsible for organizing the meeting.
谁是这次会议的主办者?
Who is the organizer of this meeting?
In this example, 主辦 again means 'to host' or 'to organize', showing that the company will take on the responsibility of executing the charity event.