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/.
iPhone 6s took the top spot as the most-shipped smartphone in the world in 2016, trailed by the iPhone 7, iPhone 7 Plus, and iPhone 6s Plus, based on research from IHS Markit's Smartphone Shipment Database, which tracks quarterly shipment data for more than 350 smartphone models.