iOS jailbreaking is
privilege escalation for the purpose of removing software restrictions imposed by
Apple on
iOS,
tvOS and
watchOS. It typically does this by using a series of
kernel patches. Jailbreaking permits
root access to iOS, allowing the installation of software that is unavailable through the official
Apple App Store. Apple publicly disapproves of jailbreaking, stating that it can cause device instability.
[1] This has led to Apple implementing hardware and software fixes to the
vulnerabilities used in jailbreaks, meaning that many versions of iOS are not jailbroken immediately. (
Source)