iOS questions are only on topic insofar as the devices interface with regular computers. Most questions about iOS devices should be asked on apple.stackexchange.com.
iOS (known as iPhone OS prior to June 2010) is Apple's mobile operating system. Originally developed for the iPhone, it has since been extended to support other Apple devices such as the iPod touch, iPad and Apple TV. Apple does not license iOS for installation on third-party hardware. As of January 14, 2011, Apple's App Store contains more than 300,000 iOS applications, which have collectively been downloaded more than 10 billion times. In the last quarter of 2010, it had a 16% share of the smartphone operating system market in terms of units sold, third behind Google's Android and Symbian. As of May 2010 it accounted for 59% of mobile web consumption (not including the iPad) in North America.