Semantic HTML means using the element that matches the meaning of the content. It sounds small, but it decides whether a blind user can navigate your page, whether search engines understand it, and whether the next developer can read your code. Interviewers notice it quickly.
Meaningful elements
Compare these two snippets:
<div class="btn" onclick="order()">Order</div><button type="button" onclick="order()">Order</button>Both look like a button once styled. But only the second one is a real button. It can be reached with the Tab key, pressed with Enter or Space, and a screen reader announces it as "Order, button". The div version does none of this unless you add a lot of extra code.
Useful elements to know:
header,nav,main,footer: the big regions of a page.h1to : headings in order. One per page, then for sections, inside those.