The <!—> is a tag for HTML comment. The notes which are commented are not seen by the browser. Basically it helps the developer to write notes about their code which will later on help them to understand the code. These HTML comments are visible to anyone who visit the source code.
HTML Comment Syntax
<!--Write Comment here...>
Note: Comment is a piece of code that every web browser ignores but, It is good practice to add the comments because it increases the readability and understandability of code.
<!-- Whatever you will write inside the comment tag will not be shown--> <p>Hello World</p>
Note: Comments are also very useful while debugging the code because programmer can switch off the other code by commenting it and check the code chunk by chunk.