Android is an open source mobile operating system developed by Google that is based on the Linux kernel. It is the most widely used mobile operating system globally. iOS is a proprietary mobile operating system created by Apple exclusively for its hardware like the iPhone, iPad, and iPod Touch. It is the second most popular mobile operating system. Android supports a wide range of devices and services while iOS only supports Apple devices and has limited availability. In terms of development, iOS is more efficient as it requires fewer programming languages than Android, but Android has better availability and adoption rates due to its wide device support.