Why is a heading important for search engine optimisation?

A heading tag appears as a title on the web page in bold.

This is a heading

To make text into a heading, the format of the text needs to be changed. Heading tags range from H1 to H6 (H1 being the largest size). Heading text is often a summary of the body text, therefore search engines place great value in finding keywords that appear in this tag.

In your HTML code a heading looks like this:

<h2>This is a heading</h2>