An untethered jailbreak is a modification that bypasses some of a device’s operating-system restrictions and remains usable after a reboot without requiring a computer or another external step to reactivate it. This differs from a tethered jailbreak, which needs an external trigger after restart.
Persistence matters because rebooting alone may not restore confidence in a device’s integrity. In attacks or security demonstrations, a jailbreak that survives restart can complicate containment and investigation, particularly if it affects protections such as code signing or the boot chain. Defenders should not treat a reboot as proof of recovery; they may need to verify device integrity and enrollment status before trusting it again. The term describes a persistence capability, not by itself proof of broader compromise.