- the backward counting in fixed time units from the initiation of a project, as a rocket launching, with the moment of firing designated as zero.
- the final preparations made during this period.
- a period of increasing activity, tension, or anxiety, as before a deadline.
- the act of counting backwards to time a critical operation exactly, such as the launching of a rocket or the detonation of explosives
- to count numbers backwards towards zero, esp in timing such a critical operation
