Which term refers to the main thought expressed by a work?

The term that refers to the main thought expressed by a work is "theme." The theme represents the overarching idea or underlying message that an author conveys throughout a piece of literature, whether it be a story, poem, or other forms of writing. Themes can explore various aspects of the human experience, such as love, conflict, identity, and societal issues.

While "thesis" is an important concept in writing, particularly in argumentative essays, it specifically refers to the writer's stance or argument rather than the broader message conveyed through the entire work. "Symbolism," on the other hand, involves the use of symbols to represent ideas or themes within the text, and “mood” pertains to the emotional atmosphere created by the work. Thus, while these terms are related to literature, the concept of theme is the most fitting answer for identifying the main thought that an author wishes to express.