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.
Categories: Space English informal noun time

'countdown' on video