iOS is a mobile phone and tablet operating system built by Apple, Inc. It is a light weight touch screen OS based on the Mac OS UNIX called Darwin.
iOS, formally known as iPhone OS, is Apple's mobile operating system. Originally developed for the iPhone, it has since been extended to support other Apple devices such as the iPod touch, iPad and Apple TV. Applications for the iOS are available from Apple's App Store which contains more than 300,000 iOS applications, which have collectively been downloaded more than 10 billion times.