You can include a comment in an HTML file. A comment will not be displayed on web page and will help you remember why you coded something in a particular way.
The comment tag is used to insert a comment in the source code. Make sure to insert two hyphens after the exclamation mark and two hyphens before the great-than sign. Let's say the comment was "This is my comment", you would type:
<!-- This is my comment. -->
You won't see the comment on the web page. It's ignored by browsers. The comment is only visible in the source code.