Jailbreak is the name to given the process used to modify the operating system which running the IPad, IPhone and IPad touch to allow the user control over the devise including remove any Apple imposed restrictions on Apple products. Hope this helped.
It means to break into an electronic device (most commonly an apple product), and change how the device runs. For example you can change how the app icons look, or how the mp3 playing part looks. You can also remove the slide to open part.
Jailbreaking allows the user access to the operating system of a device, specifically an iPod touch or iPhone. After an iPhone has been jailbroken, the owner of the device is no longer bound by apple's restrictions and can add additional apps and features onto it.
However, a jailbroken iPhone voids its warranty and some other apps may not work with a jailbroken iPhone.