iOS is Apple's mobile operating system. iOS runs on the iPhone, iPad, and iPod Touch.
Apple has sold over 120 million iOS devices. This breaks down to:
iPhone: 67.6 million
iPod Touch: 45.2 million
iPad: 7.2 million
The iPhone App Store has over 350,000 apps.
The iPad App Store has over 65,000 apps.
Apple has a 27% smartphone marketshare in the US.