Website: HTML Upload
For a standalone page that is not part of your website's structure. A one-off landing page, a file somebody asked you for, something you were given as finished HTML. Upload it and it is served from your own domain at its own address, outside the menu and outside your design. If what you want is a real page of your site, with your fonts, your colors and a menu entry, use Website then Pages instead: the result is part of the site rather than a visitor's dead end.