Extended definition
HTML tags that hierarchically structure content. H1 = main title (only one per page). H2-H6 = subtitles.
Context and application
Common myth: “one H1 per page, mandatory”. HTML5 explicitly allows multiple H1s (in <article>, <section> sections) — browsers and Google have no problems. Classic SEO tools report “multiple H1” as an error — it’s a false positive in 2026. What matters isn’t the count, but the hierarchy: never skip (H2 → H4 without H3). For AI Overviews extraction, intro paragraphs under H1 + descriptive H2s with clear definitions = optimal.
In practice
a logical H1 → H2 → H3 structure helps both the user and Google understand the page.