A God from the Machine.
It was common practice in some Greek and Roman plays to lower by means of a crane (i.e., a machine) an actor playing a god onto the stage in the last act. This god would then proceed to neatly solve all of the problems, get everyone out of trouble, and wrap up the play.
The term deus ex machina is now used to refer to any plot device that was not foreshadowed, or is not believable, or just doesn't fit, and that is used to solve any otherwise insolvable problems. Someone suddenly inherits a million dollars, the cavalry pops up in the nick of time, the Master Detective had the missing piece of the puzzle all the time.
A contrived wimp-out on the author's part.
Pronounced 'DAYes eks makena', or 'ma-kuh-nuh', or 'MAK-uh-nuh'. There are multiple acceptable pronunciations. Rose Thorn reports 'day-us aches mashina' as a correct pronunciation. Excalibre reports that the Latin pronunciation is approximately "day-oos eks mah-kee-nah".
The plural is dei ex machinis.