Multi Line comment in HTML - Basically multi line comment in HTML is not a special type of comment, it is just comment and it depends on us how we are using it. In single line comment if we include more than one line then it becomes multi line comment, see below syntax how we can insert a multi line comment in HTML
<!-- this is line 1
this is line 2
this is line 3 -->
The above example is an example of multi line comment in HTML, we just have inserted multiple lines between <!-- opening tag and --> tag, all content between these opening and closing tags will not be rendered by browser in the webpage.
It also can be used in commenting javascript code in the HTML webpage. I hope this information will help you Ankush in solving your problem. Thanks