IOS

www.apple.com/ios
iOS (formerly iPhone OS or iPhone Operating System ) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also included the versions running on iPads until iPadOS was introduced in 2019, as well as on the iPod Touch devices, which were discontinued in mid-2022. If an unauthorized user attempts to sign in using another user's Apple ID, the owner of the Apple ID receives a notification that allows them to deny access to the unrecognized device.
More at Wikipedia...