HTML Headings
Headings are defined with the <h1> to <h6> tags.

<h1> defines the most important heading. 
<h6> defines the least important heading.
Example
<h1>This is a heading</h1>
<h2>This is a heading</h2>
<h3>This is a heading</h3>

Output:
This is Heading
This is Heading
This is Heading

Use HTML headings for headings only. 
Don't use headings to make text BIG or bold.

H1 headings should be used as main headings, followed by H2 headings, 
then the less important H3 headings, and so on.