iOS is the operating system behind all Apple devices, including iPhones, and can only be found in Apple products.
An Operating system (OS) is what runs a computer, and since smartphones today are handheld computers, they have an OS as well. The operating system determines which functions your smartphone can run and how its memory gets managed. The OS is also a platform that runs applications or ‘apps’.
iOS is widely considered to be one of the most user-friendly operating systems, especially because it makes linking multiple Apple devices very easy.