What is a lesson taught by a literary work commonly referred to as?

The term that best encapsulates a lesson taught by a literary work is "moral." A moral is a specific kind of lesson that often conveys a general truth about human behavior or ethical conduct, typically stemming from a story's events and characters' experiences. In literature, morals often emerge from fables or allegorical works, where the narrative serves to impart a lesson about right and wrong.

While "theme," "message," and "principle" can also relate to interpretations of literary works, they have broader meanings or contexts. A theme refers to the underlying subject or idea explored in a story, rather than a direct lesson. Similarly, a message might encompass various interpretations and ideas conveyed by the author, not necessarily tied to moral instruction. A principle, while it can share aspects with moral lessons, often refers to fundamental truths rather than the specific learnings or ethical takeaways presented in a narrative. Hence, "moral" is the most fitting term for this specific concept of a lesson in literature.