Jailbreaking of iOS devices is usually compared to Rooting of Android devices. Although both the concepts involve escalation of privilege, they differ substantially in many scope. With few exceptions, Android devices do not implement strong technical measures to prevent the users from replacing or modifying the OS (Operating System); and enabling installation of applications that have not been authorized or reviewed by a central authority such as Google, which is a simple user preference.
In the market contrast, iOS is engineered with many strong security measures (including a 'locked bootloader') intended to prevent the users from installing applications whaich are not authorized by Apple, to prevent the user installed applications from gaining root privileges and modifying the operating system. Jailbreaking an iOS device to defeat all these security measures, presents a challenge which is technical. Jailbreaking does violates the Apple's end-user license agreement for iOS devices.