The HTML tag is used to insert a JavaScript into an HTML page.

How to Put a JavaScript Into an HTML Page

<script>
document.write("Hello World!");
</script>

The code above will produce this output on an HTML page:

Hello World!

To insert a JavaScript into an HTML page, we use the <script> tag. Inside the tag we use the type attribute to define the scripting language.
So, the </script> tag tells where the JavaScript starts and ends:

<script>
...
</script>

The word document.write is a standard JavaScript command for writing output to a page.
By entering the document.write command between the <script> and </script> tags, the browser will recognize it as a JavaScript command and execute the code line. In this case the browser will write Hello World! to the page:

document.write("Hello World!");

HTML Comments to Handle Simple Browsers
Browsers that do not support JavaScript will display JavaScript as page content.
To prevent them from doing this, and as a part of the JavaScript standard, the HTML comment tag can be used to "hide" the JavaScript. Just add an HTML comment tag (end of comment) after the last JavaScript statement.

<script>
//this is a comment
document.write("Hello World!");
</script>

The two forward slashes at the end of comment line (//) is the JavaScript comment symbol.