What is the term for the general subject that the author develops in their writing?

The term that best describes the general subject the author develops in their writing is the topic. The topic refers to the broad concept or main subject area that is being discussed or explored in a piece of writing. It sets the foundation for what the entire text will cover, guiding the reader's understanding of the context and content.

For instance, in a narrative about climate change, the topic would encompass the various facets of climate change that the author addresses. This differs from the main idea, which focuses specifically on the primary point or argument the author is trying to make about that topic. Thematic statements and illustrative examples serve different purposes—they express underlying themes or provide specific instances to support points rather than encapsulating the broader subject itself.