Jail broken

The easiest to explain it I found by McAfee: Jailbreaking is hacking of an iOS device to bypass limitations imposed by Apple, which can allow users to run applications that are not authorized by the Apple App Store. This makes your device much more susceptible to viruses and malicious applications.

Also, here is a good read where a group called Hacking Team (who were recently hacked) advised against jailbreaking an iOS device: http://www.macworld.com/article/2944712/hacking-team-hack-reveals-why-you-should nt-jailbreak-your-iphone.html