The HTML contains six types of headings which are defined with the <h1> to <h6> tags. Each type of heading tag displays different text size from another. So, <h1> is the largest heading tag and <h6> is the smallest one.

<h1>Heading no. 1</h1>    
<h2>Heading no. 2</h2>    
<h3>Heading no. 3</h3>    
<h4>Heading no. 4</h4>    
<h5>Heading no. 5</h5>    
<h6>Heading no. 6</h6> 

Heading no. 1    
Heading no. 2    
Heading no. 3    
Heading no. 4    
Heading no. 5
    
Heading no. 6