Which term best describes the main idea of a piece writing in brainpop?

The term that best describes the main idea of a BrainPop piece is "topic".

Here's why:

* Topic: This is the broad subject or theme being discussed in the video or article. It's the overarching idea that the entire piece revolves around.

* Main Idea: This is the central point or argument the author is making about the topic. It's the key takeaway or message that the writer wants the viewer/reader to understand.

While "main idea" focuses on the specific message, "topic" provides the broader context for that message. Since BrainPop pieces are designed to introduce and explain a specific topic, "topic" best describes the overall focus.