Semantic HTML introduce the meanings of a web page instead of the only presentation. A simple way to understand is
Semantic elements = elements with a meaning.
Examples of non-semantic elements: <div> and <span> – Defines nothing about its content.
Examples of semantic elements: <form>, <table>, and <article>- Clearly defines the purpose of its content.
HTML5 offers a lot of semantic HTML elements and all the modern browsers support those. Some of the semantic elements are
<article> <aside> <details> <figcaption> <figure> <footer> <header> <main> <mark> <nav> <section> <summary> <time>