Latin; literally, "God out of the machine."  Roughly synonymous with "miraculous surprise ending", an important form of catharsis.

In medieval morality plays, the plot would find the hero or heroine in a desperate and truly hopeless plight, only to be saved by the hand of God extending from the heavens or from a cloud, literally snatching them from the clutches of death. Stage machinery would effect the ersatz hand-of-God, with pulleys and ropes approximating the miracle.

A PlotEnablingDevice; it originated in AncientGreekDrama.

Effective patterns use catharthis to make the solution memorable. But see PatternsDontNeedToGoBoom.

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Funniest example of this, though not an ending:

In "Monty Python's Life of Brian", Brian is pursued by Roman soldiers to the top of a tower. Having nowhere left to go, he leaps from the tower to his death, only to fall into a passing UFO which zooms into outer space, engages in battle with another UFO, is damaged, and crash-lands at the base of the tower. As the sole survivor of the crash, Brian, climbs out of the wreckage, a beggar-woman across the street opines, "Lucky b-----d!"

-- DanHankins

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critics slam bible for DeusExMachina beginning -- from untitleddocument