Which term best describes a sudden and improbable resolution to a problem in a story?

The term that best describes a sudden and improbable resolution to a problem in a story is "Deus ex machina." This term originates from ancient Greek theater, where a god would be introduced into the plot to resolve complex situations or conflicts that seemed impossible to overcome through the characters’ actions alone. In contemporary literature, it refers to any unexpected or contrived resolution that simplifies the narrative conflict, often with little build-up or logical transpiration.

In contrast, foreshadowing involves hints or clues about future events in a story, and so does not describe a sudden resolution. The terms protagonist and antagonist refer to the main character and the opposing force, respectively, and do not relate to the concept of resolution at all. In summary, "Deus ex machina" captures the essence of an improbable resolution effectively, distinguishing itself from the other terms provided.