The Pangu group has released a new jailbreak for 64-bit iPad and iPhone devices running iOS 9.1, including iPhone 6s and iPhone 6s Plus.
Jailbreaking circumvents internal security measures put in place by Apple to protect an iOS device, thereby allowing third party software to be installed and other modifications to the device. While this activity is popular with a subset of advanced users, the vast majority of iPhone and iPad owners should not jailbreak their devices, as jailbreaking can void the device warranty, lead to potential security issues, and generally offer a less stable iOS experience. That, in addition to many other reasons not to jailbreak an iPhone or iPad, can be read here. This is truly for advanced users only and is not recommended for most. Unsurprisingly, Apple also strongly opposes jailbreaking.
If you happen to be interested in jailbreaking, have made a backup of your iOS device, and happen to be running iOS 9.1 on a compatible iPhone or iPad, you can get Pangu from the developer site here. The Pangu 9.1 download is about 70mb.
The Pangu 9.1 tool is available for both Mac OS X and Windows, and also supports jailbreaking iOS 9 on earlier 32-bit devices. The actual process of jailbreaking is typical of a Pangu release for those familiar with the procedure, involving backing up the device, turning off Find My iPhone, connecting it to the computer with USB, launching the Pangu app, and walking through the various steps shown on screen.
There is no way to downgrade iOS to prior final releases, so if you have already moved beyond iOS 9.1 as most likely have, this utility will do nothing for you. The current version of iOS is 9.2.1, and iOS 9.3 is expected to be available to the public in the coming weeks.
Separately, the Pangu group also mentions a jailbreak for the Apple TV 4th generation will be available soon as well.