Defintion (deus ex machina)- The term has evolved to mean a plot device whereby a seemingly unsolvable problem is suddenly and abruptly resolved by the contrived and unexpected intervention of some new event, character, ability or object. Depending on how it is done, it can be intended to move the story forward 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.
...I love when Death appears on SPN, but I am having a hard time not having this in my mind the entire time...not really a discussion topic, just felt like saying it