CSS comments are the same as what you must have learnt in any technical language. It is written to explain the code and is helpful for the users who read that code so that they can understand it easily.
In technical terms, it is known as a selector. It tells the browser on which portion of the HTML document the styling needs to be applied.
Comments are ignored by browsers, and the syntax to write them is:
<style>
/* Cascading Style Sheet Comments */
</style>