HTML Comments:

The comment tags <!-- and --> are used to insert comments in HTML file.

Example:

<p>This is a paragraph.</p>
<!-- Add your comment here. -->

<!-- Do not display this at the moment
<img border="0" src="abcfile.jpg" alt="Name">
-->

Conditional Comments:

<!--[if IE 8]>
    .... some HTML coding here if you want ....
<![endif]-->