What term refers to the subject of a text, or what the text is about?

The term that refers to the subject of a text, or what the text is primarily about, is "topic." The topic serves as the overarching idea or the main focus around which the content is organized. It provides a foundation for understanding the specific details, examples, and arguments presented in the text.

In contrast, the theme refers to the underlying message or moral that the author communicates through the text, while the main idea is a more specific statement that captures the primary point being made in a particular section or the entire work. Supporting details, on the other hand, are the facts, examples, or arguments that help to elaborate and reinforce the main idea. Understanding the topic is essential for grasping what the text is conveying and facilitates a deeper comprehension of its themes and main ideas.