What does it mean to jailbreak an iPhone?

What's the different between a jail broken iPhone and a not jail broken iPhone?

It allows you to install apps that aren't approved by apple. You won't need to get all your apps from the iTunes store.

A jailbroken iPhone is a iPhone which third-party software has been installed to. This can allow extreme customization to be done to the iPhone using themes. You can get Themes, tweaks, and more using Cydia (http://cydia.saurik.com/). Jailbreaking will allow you to install Cydia to your Phone. I would not recommend this. It slows the phone down and can cause permeant damage. Apple products just work, Installing thirdparty garbage is a mistake.

Jailbreaking an iPhone unlocks your phone to its full potential. You get a new app store with apps you couldnt get with an iPhone when its not jailbroken. The bad thing about that is if your iPhone shuts down or breaks you can't get anyone to fix it because the phone people don't like it when you jailbreak your iPhone, iPod, or iPad. I hav an iPod i got from a friend and i jailbroke it but i didn't jailbreak my iPhone just in case something happens to it.

It's like letting your iPhone be free lol. Apple no longer has nothing to do with your phone. Well they do, but you can control it. Do whatever you want to it. You can turn it to an android phone if you wanted to.

You can get free apps and games.