In 2007 JailbreakMe was a popular way to jailbreak your iOS device. It used a web site and a flaw in Safari to insert apps and the Cydia app store into your iOS phone or tablet, and it worked well for a while.
JailbreakMe is a really old school jailbreaking scheme from around 2007 to 2011 that's not really used anymore as the firmware was changed to close the loophole it used to get into iOS. That was the end of the story until recently.
Users of the iOS 9 Pangu jailbreak found a new use for the JailbreakMe methods to solve an update which caused their certificates to expire. Let me explain, the Pangu jailbreak uses your Apple ID to digitally sign the security certificates that allow you to "sideload" software into your iPhone.
Sideloading is a term borrowed from the Android community and means installing software from sources other than Google Play, like slipping it in under the door. This is only possible if the user has enabled software from "unknown sources" in their security settings. Obviously on iOS this is not possible without careful sidestepping of the inbuilt security.
Anyway, so Pangu was working well as a jailbreaking option but the tricky certificates were expiring which meant that users who jailbroke with Pangu had to repeat the process, wiping everything to get back to normal. Very annoying. The neat fix they came up with was a nostalgic nod to the JailbreakMe method which uses a web page to jailbreak the device.
Instead of users being forced to delete the Pangu app and reboot the iPhone into non-jailbreak mode and redo the whole jailbreak, a programmer called Luca Todesco came up with a workaround. Instead of jailbreaking the device the web page allows Pangu users to renew their security certificates without reinstalling.
Although this is a mostly trouble free way to jailbreak your iOS device, of course there are rare occasions when for no fault of yours, the process gets interrupted and your iPhone gets frozen or on reboot it gets confused and gets locked in a loop. If this happens to you it's wise to have some utility software on hand to fix your iPhone.
Plus the ever present risk of jailbreaking your iPhone or other iOS device is that apps you can load from Cydia don't go through the rigorous quality assurance that official App Store Apps do. They can crash and cause other problems. Not often, for sure, but it can happen.
Tenorshare ReiBoot is a small and simple app which unfreezes your iOS device and places it into recovery mode so to fix various iOS stuck issues. If you wish for a small fee you can upgrade to Tenorshare ReiBoot Pro which fixes 50+ iOS problems at the click of a button, and does so totally free of the influence of iTunes.
This is vital insurance if you like to jailbreak your iPhone to enjoy a world of apps outside the Apple ecosystem. Play safe out there.