What is iOS? The iPhone operating system is abbreviated as IOS. It is Apple's own mobile operating system for its portable devices. The programming languages Objective-C, C/C++, and Swift are all supported. It is based on the Macintosh OS X operating system. It is the world's second most popular mobile operating system, after Android. This operating system is used by several of Apple's mobile devices, including the iPhone, iPad, and iPod. iOS uses a multi-touch interface to control the device, ...