Jailbreak

Jailbreaking is the process by which Apple’s operating systems are modified to remove restrictions and give the greater user control over the device.
These modifications typically allow running unsigned code, as well as reading and writing to the root filesystem, both of which are normally prevented by Apple. The increased privileges permit customizations and unfettered app installation which are not available to users with a stock device. Jailbreaking is most popular on, and most associated with, Apple’s mobile operating system iOS, though it also exists on tvOS and watchOS.