It means to install a app that is not found in app store called CYDIA and in that app you can get games and hacks for free like you can get paid games free or you can click buy item and buy it without having to put any details or submit anything! but it is only for I-PRODUCTS versions below 6.1.3
Ok... "Jailbreak" is a method used to instal a open source application called "Cydia", it is similar to the AppStore except, it offers more customization and more freedom, towards your device. Since "Cydia" cannot be downloaded from the AppStore or simply through web, because of security reasons and also because apple has denied such hacking. They created a method / bypass so you can instal "Cydia". It is basically hacking but it's legal! People got confused on wether jailbreaking and unlocking. Unlocking is used ONLY for phones... It's a method used so you can use your phone or activate it, without needing a service / carrier to do it so. Jailbreaking Is for ALL iDevices. There has been also rumors that jailbreak has ruined their device, which I state partly false. The barebones "jailbreak" does not do such thing, jailbreak was originally created only for customization ( since apple does not let us customize ) such as Ringtons, wallpapers, tweaks, applications, Dev tools, and so on. The people have tool full opportunity of this jailbreak being open source, that they have created a lot of pirating stuff, which got out of hand and began stealing applications from both Cydia and AppStore... Cause "Cydia" originally sold their products... Now it's being pirated... But it's legal.. - Hope this helped! If you have more questions please do reply or email me ( located in my profile info ) Have a nice day!