Deus ex machine

Deus ex machina (Latin: [ˈdeʊs ɛks ˈmaː.kʰɪ.naː]: /ˈdeɪ.əs ɛks ˈmɑːkiːnə/ or /ˈdiːəs ɛks ˈmækᵻnə/; plural: dei ex machina) is a Latin calque from Greek ἀπὸ μηχανῆς θεός (apò mēkhanês theós), meaning "god from the machine". The term has evolved to mean a plot device whereby a seemingly unsolvable problem is suddenly and abruptly resolved by the inspired and unexpected intervention of some new event, character, ability or object. Depending on how it is done, it can be intended to allow a story to continue when the writer has "painted himself into a corner" and sees no other way out, to surprise the audience, to bring the tale to a happy ending, or as a comedic device.

...
Wikipedia