N-COUNT
前奏；序幕；开端
You can describe an event as a prelude to a more important event when it happens before it and acts as an introduction to it.
例句
Most unions see privatisation as an inevitable prelude to job losses...
大多数工会认为私有化会不可避免地导致失业。
The conference, which closed yesterday, was a prelude to a Communist Party Central Committee meeting.
昨天结束的会议拉开了共产党中央委员会会议的序幕。