The trailing letter in iOS stands for “system.” The acronym represents the iPhone Operating System, a proprietary mobile operating system created and developed by Apple Inc. specifically for its hardware. As an example, iOS manages hardware resources and provides the fundamental services upon which applications run on iPhones, iPads, and iPod Touch devices.
The inclusion of “system” highlights that this software is more than just a collection of apps; it is a comprehensive platform managing all aspects of the device. The name reflects the tight integration between the hardware and software, providing a consistent and optimized user experience. Its historical roots trace back to the original iPhone launch, marking a significant shift in mobile computing. This system has enabled a rich ecosystem of applications and services.