countdown

详细解释:n. 倒计数
【电】 指示串联中的操作数固定的记录减少

英语解释：

名词 countdown:

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

详细解释：

count.down

n.（名词）
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.
倒数报时：从任意的一个数字开始倒着数，以表明距离某件事或操作（例如发射导弹或宇宙飞船）的时间
The checks and preparations carried out during this activity.
准备过程，准备工作：在倒数报时期间所进行的检查和准备