The coding language primarily used for developing iOS applications is Swift, a language introduced by Apple that is both user-friendly and powerful. Swift allows developers to write clean and efficient code, facilitating better performance and security in applications. It has largely replaced Objective-C, the former primary language, due to its modern syntax and enhanced features. Swift also integrates seamlessly with Apple's development tools, such as Xcode, making it easier to design, test, and deploy applications across Apple devices, including iPhones and iPads.