Arbitrary Pages are pages that do not have product on them. Examples are a 'Contact Us' page, 'Support', 'News', etc.
We also use them to put our css and js files on the server. That makes them easy to edit, and we don't have to FTP them to the server, which can be painful for frequently changing files.
Within our template files, you will see some inconsistency between using arbitrary pages and upload css and js files via ftp to the assets directory. Well, it's a work in process, and if someone is hacking on a style, they'll keep it as an arbitrary page, then ftp it onto the server when it's less volatile.
Ignore the aws.html file. It's a playground file.
The source for the files above are attached to this page.