Countdown
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A countdown is the backward counting to indicate the seconds, days, etc. remaining before an event occurs or a deadline expires. Typical events for which a countdown is used include the launch of a rocket or spacecraft, the explosion of a bomb, the start of a race, or the New Year.
In the context of a rocket launch, the "T minus Time" is the time before launch, e.g. "The countdown was held at T minus 5 minutes for 3 minutes and 40 seconds". The last ten seconds are usually counted down aloud "10, 9, 8, 7, 6, 5, 4, 3, 2, 1, Lift off!"
The first known use with respect to launching a rocket occurred in Fritz Lang's 1929 film Frau im Mond. In the film, after each number the words "seconds to go" was repeated.
When counting down to the launch of an explosive, e.g. when testing a new model of gun, it is customary to omit "5" from the countdown sequence because "five" sounds too similar to "Fire!".
At the start of old British films, the pre-title countdown sequence leading up to the actual start of the film would go: "10 NINE 8 7 SIX 5 4 3" in one-second intervals. The 6 and 9 are spelt out to avoid confusion in case the film is put in upside-down. The American film countdown has a different look. The countdown ends at three so that the countdown isn't shown if the film is put on screen a little earlier than intended. Although this sequence was usually not intended for broadcast, being a cue device for a projectionist or TV producer, it is often used in modern-day spoofs to signify old film footage.
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