Final answer:
The main idea refers to the central message or theme of a piece of writing, while the topic is the subject or content that the writing is about.
Step-by-step explanation:
The topic and the main idea are two distinct concepts. The main idea refers to the central message or theme of a piece of writing, while the topic is the subject or content that the writing is about. For example, in a story about the effects of poverty, the main idea might be that poverty can have detrimental effects on individuals and society. The topic would be poverty itself.
While the main idea is generally a broader concept, the topic is more specific and focuses on the subject matter of the writing. It is important to understand the main idea to get a sense of the overall message of the writing, while the topic helps to provide more context and details about what is being discussed.