Other forms: jailbreaks
A jailbreak is a prison escape. Whenever someone who's incarcerated or locked up manages to get out illegally, that's a jailbreak.
Prison security, from armed guards to razor wire, locks, and security cameras, means that jailbreaks don't happen often. These days it's more common to use this word to talk about computers or smartphones. When a hacker performs a jailbreak on one of these devices, she bypasses the manufacturer's restrictions so that even unauthorized software can be installed.