The document discusses iOS, the operating system developed by Apple for use on its mobile devices. It notes that iOS was originally designed for the iPhone but now supports additional Apple products like the iPod Touch, iPad, and Apple TV. Over time, iOS has continued to be updated and new versions released, adding new features, apps, and supporting additional Apple devices. As of 2011, the App Store contained over 500,000 iOS applications that had been downloaded over 30 billion times.