Touch ID is a function on some of Apples iPhone, which allow the user to unlock their phone by fingerprint recognition.  The function was released in 2013 with the iPhone 5s. Touch ID has also been used on Apples iPads and MacBook.   I personally think the function is great as it allows me to open the phone extremely quick if I want to. This is a feature that can be helpful if you for example want to take a photo of something and need to do it quick.