A 'Deus Ex Machina' (literally "god out of a machine") is an improbable contrivance in a story. The phrase describes an artificial, or improbable, character, device, or event introduced suddenly in a work of fiction or drama to resolve a situation or untangle a plot.
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Antithesis to the more commonly known Deus Ex Machina, Diaboli Ex Machina ("devil out of a machine") represents an improbable dissolution instead of a resolution, an unanticipated unraveling of both thought and form.
(...or not)
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The Latin phrase "deus ex machina" has its origins in the conventions of Greek tragedy. It refers to situations in which a mechane (crane) was used to lower actors playing a god or gods onto the stage. Though the phrase is accurately translated as "God from a machine," in literary criticism, it is often translated to "God on a machine." The machine referred to in the phrase is the crane.