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

HTML 5 <noscript> tag

Definition and Usage

The <noscript> element is used to define an alternate content (text) if a script is NOT executed.

The <noscript> element does not do anything, but is used for browsers that recognizes the <script> tag, but does not support the script in it.

Differences Between HTML 4.01 and HTML 5

None

Tips and Notes

Note: If a browser supports scripting, it will not display the text in the noscript element.

Note: Browsers that do not recognize the <script> tag will display the tag's content as text on the page. To prevent the browser from doing this, you should hide the script in comment tags. An old browser (one that does not recognize the <script> tag) will ignore the comment and will not write the tag's content on the page, while a new browser will understand that the script should be executed, even if it is surrounded by comment tags!

Examples

JavaScript:
<body>
...
...
<script type="text/javascript">
<!--
document.write("Hello World!")
//-->
</script>
<noscript>Your browser does not support JavaScript!</noscript>
...
...
</body>

VBScript:
<body>
...
...
<script type="text/vbscript">
<!--
document.write("Hello World!")
'-->
</script>
<noscript>Your browser does not support VBScript!</noscript>
...
...
</body>

Try-It-Yourself Demos

Work with browsers that do not support scripts
How to handle browsers that do not support scripting.

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