An HTML comment:
The comment tag is used to insert comments in the source code. Comments are not displayed in the browsers.
You can use comments to explain your code, which can help you when you edit the source code at a later date. This is especially useful if you have a lot of code.
You can also use the comment tag to "hide" scripts from browsers without support for scripts (so they don't show them as plain text):
The comment tag does not support any standard attributes.
More information about Standard Attributes.
The comment tag does not support any event attributes.
More information about Event Attributes.