iOS (previously known as iPhone OS) is a mobile operating system made by Apple Inc., which is designed for use on its mobile devices, the iPhone, iPad, and iPod touch. As of February 2013, the latest version of iOS is 6.1.2.
When the original iPhone was released, Apple did not officially name the software but simply stated that iPhone runs a version of OS X. With the release of the iPhone 3G and the software version 2.0, the operating system was named iPhone OS. With the release of version 4.0, iPhone OS was renamed to iOS since the operating system was not running exclusively on the iPhone anymore.