The extension .html is a standard extension for web pages created in HTML (Hypertext Markup Language). The .htm extension is a variation of the same extension that you can use for your website files.By default, the page you'll see when you visit your web address is index.html. If you don't have an index.html file, our servers will look for a file called index.htm. If your website does not contain either of these files, you will get a warning, and your website visitors will see an error if they try to visit your web address. If you are not using the standard index.html