iOS is Apple's mobile operating system used to run the popular iPhone, iPad and iPod Touch devices. Formerly known as the iPhone OS, there are over 300,000 iOS applications available for download in the Apple app store, the most popular app store of any mobile device. iOS utilizes a multi-touch interface where simple gestures are used to operate the device, like swiping your finger across the screen to move to the next page or pinching your fingers to zoom out.
Since its release, iOS has gone through multiple updates, with recent updates adding the ability to create folders for app icons and the ability to multi-task. The updates are generally free for iPhone and iPad users, while iPod Touch users are sometimes required to pay a nominal fee.
Updates to the iPhone, iPad and iPod Touch are done through the iTunes software package, which is a free download for Mac OS and Windows.