Hi ALC, deus ex machina is Latin, not French, and it means god/deity out of the machine, the expression is also used in English. It is an allusion to Greek and Latin plays in which a god suddenly appeared to solve a difficult situation.
Here is a more detailed explanation: http://newark.rutgers.edu/~jlynch/Terms/deusexmachina.html
You'll come across the deux ex macina in plenty of English-language literature as well. Some of Poe's works for example. Various movies as well. In those cases, it's an heroic character who "comes to the rescue."