What does the "AI rewrite" label on a chapter mean?

From version 1.9.21, when the AI rewrites a chapter you wrote yourself (with the wand button on an imported book, or with "Regenerate all"), the chapter gets a small "AI rewrite" label with the kind of rewrite, for example "AI rewrite · Polish". Amazon KDP counts text rewritten by AI as AI-generated content, and asks about it when you publish. The label tells you which chapters to count when you answer that question. Put the chapter's original text back from its Versions panel ("Your original") and the label goes away.