App Transport Security is a feature that improves the security of connections between an app and web services. The feature consists of default connection requirements that conform to best practices for secure connections. Apps can override this default behavior and turn off transport security.

Transport security is available on iOS 9.0 or later, and on OS X 10.11 and later. Source

What does that mean?

That unless you change something in your iOS app’ plist, your app will not be able to communicate with unsecure HTTP servers, when it runs on iOS 9.

That’s a good thing really; Apple is trying to force people to update their HTTP servers to use the latest HTTPS protocols & recommendations: TLS 1.2, SHA256 or better, forward secrecy.