What does Jailbreak App mean?
A jailbreak app is a third-party application that is installed and used on devices that usually restrict users to applications with the application's brand. The installation of these applications involves a process of removing limitations imposed by the device's operating system.
Usually, this term is used to refer to the mobile OS for Apple-manufactured devices (iOS). The process of circumventing OS limitations so that jailbreak apps can be installed is called jailbreaking.
Techopedia explains Jailbreak App
Users with devices running on Apple’s iOS (sometimes referred to as iDevices) are usually restricted to applications supplied by a specific brand. Through jailbreaking, they become able to install additional applications to the user's iDevice. The first of these methods, which allowed user-defined ringtones and wallpapers to be installed, was released in June 2007.
Shortly thereafter, the first jailbreak application was released. It was a third-party game for the iPhone and iPod Touch. Since then, there has been a cycle of improvements from Apple developers to try to prevent such methods from being used on their devices, as well as prevent so-called computer hackers or jailbreakers from developing new jailbreak methods to override each new iOS version.
There are a variety of jailbreak apps, which can be downloaded through various sources. Through an application that allows for the addition of these jailbreak apps (like Cydia), iDevice users are allowed more freedom to add to their device's capabilities. Although similar to the in-stock App Store option, Cydia allows the installation of applications not produced or accredited by Apple.
Jailbreak apps allow users to add games, personalize the appearance of their iDevices (like changing themes, chat bubbles or even the dialer keypad) and add many more applications.