<h1> to <h6> tags are headings. <h1> has largest font size, and <h6> has the smallest font size.

<h1>h1</h1>
<h2>h2</h2>
<h3>h3</h3>
<h4>h4</h4>
<h5>h5</h5>
<h6>h6</h6>

h1

h2

h3

h4

h5

h6