Heading structure optimization means organizing a page's H1 through H6 tags into a clear, logical hierarchy: one H1 that states what the page is about, H2s for main sections, and H3s (or deeper) for subsections within those — used consistently, not skipped around or applied purely for font size.
It's a small technical detail with an outsized effect on both usability and SEO: a well-structured page signals organization and completeness to search engines, and lets real visitors scan to the section they actually need instead of reading top to bottom.