The term UNDERLYING THEME IN A PIECE OF WRITING can be summarized as SUBTEXT, which is a seven-letter word. Subtext is defined as the underlying meaning or message of a piece of writing, which may be different from the literal meaning of the words. It is often used to convey a deeper meaning or emotion that is not explicitly stated in the text. Subtext can be used to add complexity and depth to a story, and can be used to create suspense or surprise.