Before you actually jailbreak, it is better to know about the difference between a tethered and an untethered jailbreak.
The one thing you should know is that Jailbreaking actually modifies the root of
your iDevice. This helps apps and tweaks from Cydia to be installed on
your iOS device which would normally not be allowed.
The way your jailbreak setup works when you reboot your iPhone is the criteria that decides whether your jailbreak is a tethered one or an untethered one.
1). Tethered Jailbreak
A tethered jailbreak is mostly the first
type of jailbreak that arrives on the web whenever a new iOS is
released. The tethered jailbreak has all the characteristic features of
an untethered jailbreak but the only difference is, you can’t reboot
your iOS device without connecting it to the computer and using a
specific tethering software (like Redsn0w).
For obvious reasons, if you have a tethered jailbreak
on your iPhone, you’ll think twice before trying to reboot your gadget.
It’s not as cumbersome as it sounds but anything that has more than one
step will, in comparison to the usual reboot process, be complicated.
2). Untethered Jailbreak
After the devs create the tethered
jailbreak and test it out, it’s time to patch things up and figure out a
way to create the untethered. And it simply means: you can reboot your
iPhone just as normally as you would, without having to connect it to
your computer or run Redsn0w’s Just Boot.
People prefer untethered – and some even wait for it till they jailbreak their iPhones – because it’s complete. Having to use a computer and Redsn0w
just to reboot often sucks because what if your iPhone got turned off
(low battery, may be?) when you are away from any access to a computer?
So that’s about all the difference there is between a tethered and untethered jailbreak.