The equals sign means is equal to. It is telling us that one thing equates to another; that they are the same.
The iPhone 4 is the most recent iPhone to be discontinued from the iOS Update cycle. It did not receive the iOS 8 update, so it's final software version is iOS 7.1.2. You can update to this version through iTunes, or download it from an IPSW repository like this website: https://ipsw.me/.
2013 - iPhone 5s. 2015 - iPhone 6s and iPhone 6s Plus. The next iPhone is expected to be called the iPhone 7. 2015 marked an S iPhone upgrade year that introduced new features such as an improved camera and a better processor, but 2016 will bring an even-year upgrade that will likely include an all-new iPhone design.