What's the difference between a tethered and an untethered jailbreak?

I know one means if you restart the iPhone, it will get stuck on the apple logo during reboot. I want the one where you can restart it with no problems and I won't have to lose any data

Untethered is what you'd want then.

Difference being when you restart you'd have to connect (tether) your iPhone to a computer & run the software for it to reboot properly. Wouldn't lose data doing that though, just a little inconvenient

"I will answer your question till then, If you need some advanced security program for your device do install Leo Privacy Guard to make it utmost secure and also you would be amazed to know that it is included in world's top ten apps.

A tethered jailbreak requires the iOS device to be plugged into a computer when turned on. If the iPhone is not plugged into a computer and booted with special software the device will not enter a jailbroken state.

Untethered jailbreaks do not require a computer. Everything required to enter the jailbroken state is contained on the iPhone. Rebooting away from a computer does not affect the jailbreak. IOS 4.3.3 and older jailbreaks including PwnageTool, limera1n, greenpoison and snowbreeze are untethered solutions."