count‧down /ˈkaʊntdaʊn/ noun [countable usually singular]

1. the period of time before something happens, such as a spacecraft being launched, when someone counts backwards until the event happens

2. the period of time before an important event, when people become more and more excited about it
countdown to
the countdown to the World Cup

[TahlilGaran] Dictionary of Contemporary English ▲

countdown
n.. Space English, informal
1. A step-by-step process which leads to the launching of a rocket.
Countdown starts at 23:00 hours tomorrow night and continues for 24 hours.
2. Process of counting inversely during the acts leading to a launch; liftoff occurs at zero.
3. The time immediately preceding an important undertaking, borrowed from Space English.
We're leaving for Hawaii tomorrow afternoon; this is countdown time for us.

[TahlilGaran] English Idioms Dictionary ▲