What is S3 storage?

It's a storage agnostic protocol for sending, receiving and enumerating to/from cloud storage. Think off it like email. Email service providers allow for a number of ways to access your email, be it pop3, IMAP or web. The underlying technology is abstracted away. In the same way cloud storage allows for web, s3 and/or WebDAV. Amongst others. And likewise the back end is abstracted away. The s3 client you use doesn't need to know how the data is actually stored. And there's some pretty whacky storage back ends.