Which term best defines the central idea or message conveyed by a literary work?

The term that best defines the central idea or message conveyed by a literary work is "theme." The theme encapsulates the underlying meaning or main idea that the author explores throughout the narrative. It goes beyond the surface-level actions and events of the story to delve into deeper philosophical or moral questions, offering insights into human nature, society, or life itself.

For instance, in a novel, the theme might revolve around concepts like love, betrayal, or the quest for identity, prompting readers to reflect on these universal experiences. By contrast, motifs are recurring elements or symbols that reinforce the theme but do not themselves represent the main idea. Symbols are specific objects or images used to represent larger concepts, while topics are simply the subjects that the work discusses—these do not encompass the deeper exploration that themes provide. Therefore, "theme" is the most fitting term when identifying the central message within a literary work.