Glossary /On-page & content
Heading Hierarchy
The nested structure of H1 to H6 elements that gives a page an outline, used by assistive technology and by parsers alike.
Headings are structure, not styling. A correct hierarchy has one H1 naming the page, H2s for its main sections, and H3s nested under those — an outline that can be read on its own and still make sense. Screen reader users navigate by it directly, which makes it an accessibility requirement before it is an SEO one.
The parsing benefit follows from the same property. Systems that extract passages from a page — featured snippets, AI summaries, retrieval systems chunking documents — use headings to decide where one idea ends and the next begins. A page with a clean outline gets quoted in coherent pieces; a page where headings were chosen for font size gets quoted badly or not at all.
The common faults are a page with no H1, several H1s competing, or levels skipped because H4 happened to look right. All three are cheap to fix and each one degrades both the accessibility and the machine reading of the page.