The reason it is called "iOS 2" is that it was the second major release of Apple's mobile operating system initially named iPhone OS, before being renamed iOS. Released on July 11, 2008, iPhone OS 2 introduced key features like the App Store, allowing third-party applications to be officially available on the iPhone and iPod Touch for the first time. This version also brought various improvements such as push email, support for Microsoft Office attachments, multiple calendar support, parental controls, and Wi-Fi enhancements. It was called "2" because it followed the original iPhone OS 1, marking a significant new version of the software.

In summary, "iOS 2" refers to the second iteration of Apple's mobile operating system, notable mainly for launching the App Store and expanding the platform’s capabilities beyond the initial release.