To get out of a restricted mode of operation. For example, jailbreaking may enable content with digital rights to be used on any computer, or it may allow enhanced third-party operating systems or applications to be used on a device.

A Lot of iPhone Jailbreaking
The term often refers to gaining access to the iPhone's file system, which is normally restricted. It enables modifications to the look and feel of the iPhone and allows applications to be installed that are not available through Apple's App Store (see Cydia). It also lets users "unlock" the phone for use with another GSM carrier (see SIM lock). See DRM and walled garden.