App Transport Security (ATS) is a feature that was introduced with iOS 9 and OS X version 10.11 back in 2015. The security enhancement forces applications to transfer data via secure connections through HTTPS - which is a more fortified iteration of the HTTP protocol. Previously, Apple had stated that ATS would be made mandatory from January 1, 2017, but now it appears that the company is extending its deadline.

It is important to note that Air Transport Security is switched on by default in Apple's development toolset, but app developers currently have the option to disable the feature. Although initially slated to be enforced starting next year, Apple is now extending the deadline. In a brief statement on its website, the company states that:

App Transport Security (ATS), introduced in iOS 9 and OS X v10.11, improves user security and privacy by requiring apps to use secure network connections over HTTPS. At WWDC 2016 we announced that apps submitted to the App Store will be required to support ATS at the end of the year. To give you additional time to prepare, this deadline has been extended and we will provide another update when a new deadline is confirmed.
HTTPS is a protocol that is extensively used for secure data communication over the internet, and is also utilized by banks and other companies dealing with private and sensitive data. That said, it'll be interesting to see how long Apple is giving developers to respond to this new deadline to update their apps - once it is announced, that is.