A comment in HTML is an area of text that is ignored by the browser. In an HTML comment, you can write anything. These are some examples of comment.

<!-- This is a comment -->
<!-- I love HTML -->
<!-- London bridge is burning down -->

Comments written in angle brackets with an exclamation mark at the start followed by two hyphens (minus sign) and ending with two hyphens.

Reasons for comments

Comments in HTML are conventionally used as:

A directive to show viewers of the source code what it does
To insert information about the document that viewers of the source code should know such as license and author's information