From wikipedia:
A deus ex machina (Latin IPA: [ˈdeːus eks ˈmaːkʰina] (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 (such as an angel suddenly appearing to solve problems).