名詞 countdown:

1. counting backward from an arbitrary number to indicate the time remaining before some event (such as launching a space vehicle)

count.down

n.（名詞）
The counting backward aloud from an arbitrary starting number to indicate the time remaining before an event or operation, such as the launching of a missile or space vehicle.
倒數(shù)報時：從任意的一個數(shù)字開始倒著數(shù)，以表明距離某件事或操作（例如發(fā)射導彈或宇宙飛船）的時間
The checks and preparations carried out during this activity.
準備過程，準備工作：在倒數(shù)報時期間所進行的檢查和準備