From http://www.w3schools.com (Copyright Refsnes Data)

HTML <!--...--> tag

Example

An HTML comment:

<!--This is a comment. Comments are not displayed in the browser-->

<p>This is a paragraph.</p>

Try it yourself!

Definition and Usage

The comment tag is used to insert a comment in the source code. A comment will be ignored by the browser. You can use comments to explain your code, which can help you when you edit the source code at a later date.

You can also store program-specific information inside comments. In this case they will not be visible for the user, but they are still available to the program. A good practice is to comment the text inside scripts and style elements to prevent older browsers, that do not support scripting or styles, from showing it as plain text.

Attributes: NONE

From http://www.w3schools.com (Copyright Refsnes Data)