The H1 is the primary heading of a page, marked with <h1>. Best practice is one H1 per page — the dominant heading that announces what the page is about to both users and search engines. Subordinate headings use H2 / H3 / H4 in semantic hierarchy.
The H1 and the title tag serve different surfaces. Title tag = SERP. H1 = the page itself. They should match in topic but can diverge in framing. A title might be optimized for CTR ("Free AEO Audit — 99 Checks in 30 Seconds") while the H1 is optimized for on-page clarity ("Audit Your Site for AI Search Visibility"). Both target the same primary keyword.
Multiple H1s per page is no longer a technical SEO violation in 2026 — HTML5 spec allows it and Google's documentation explicitly says multiple H1s are fine. But one H1 per page remains the strongest convention for clarity, accessibility, and CMS-template consistency. Stick to one unless there's a specific reason to use multiple.
For AEO, the H1 is also a critical signal. AI engines treat the H1 as the canonical page topic and weigh content extracted near it more heavily. A direct-answer paragraph immediately below the H1 is the highest-leverage placement for AI-citation candidacy.