What is a jailbreak?
Jailbreaking your device means installing a small program that removes restrictions in the default software. A jailbroken device can run apps and extensions (themes and tweaks) not approved by Apple. Jailbreaking does not slow down your device or use extra battery, and you can still use all your existing apps and buy new ones from the App Store. Jailbreaking simply enables you to do more with your device, nothing is taken away.
What are Types of jailbreak?
2. Untethered jailbreak [Read the difference between the two here]
Is Jailbreak reversible?
Yes! If you ever decide that you want to undo your jailbreak, connect your device to your computer, sync to make a full backup, press Restore in iTunes to wipe the device, and load your backup when prompted. All your App Store apps and the information in them will be preserved as usual.
Can jailbreaking "brick" my device?
Jailbreak is safe that cannot put your device into an unusable state on its own. You will have full access to your jailbroken device, which gives you the power to modify it in ways that can put it in a state where you have to connect your device to iTunes and "restore" from a recently-synced backup. However, it should not be possible to render your device as permanently non-interactive as a brick, no matter what you choose to install.
Is jailbreaking iOS devices legal??
The Library of Congress approved a DMCA exemption in 2010 for jailbreaking cell phones, including the iPhone.
Can jailbreaking make my device less secure?
By itself, jailbreaking does not make you vulnerable. However, a common mistake for jailbreakers is to install OpenSSH but forget to change the passwords for root and mobile; this lets anyone log into your device over the Internet. If you install OpenSSH, remember to change the password!