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/.
The latest version of the iPhone and iPad operating system is iOS 10, although there have been a few updates since its launch in September 2016. The current version is iOS 10.3.1. iOS 10 has proved popular since its release. As of 4 January 2017, just under four months after iOS 10's release, Apple reported that 76 percent of active iOS devices are running version 10, with 18 percent on iOS 9 and just six percent on iOS 8 or older versions.