Semantic HTML conveys meaning to assistive technologies.
Use semantic elements:
<!-- Good -->
<button>Submit</button>
<nav>...</nav>
<main>...</main>
<!-- Bad -->
<div onclick="...">Submit</div>
<div class="nav">...</div>
Benefits:
- Screen readers announce element types
- Keyboard navigation works automatically
- Browser features work (form submission, focus)
Common semantic elements: header, nav, main, article, section, aside, footer, button, input, label.