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/.
Find out what features the latest update to iOS brings to the iPhone and iPad operating system. The current software that runs on iPads and iPhones is iOS 10. iOS 10 was first announced and previewed at WWDC 2016 in San Francisco on 13 June 2016 and then released to the public on 13 September.