IOS is the operating system developed by Apple, the company behind the successful iPhone, iPod, iPad, and iMac. All mobile devices developed by Apple run on iOS, not only all iPhones but also the iPad. The desktop devices (PCs) run on macOS. The iOS operating system is written in Objective-C and the Swift programming language and, unlike Android, is closed source. This means that the operating system is not accessible for programming. Apple is further developing the system itself, the versions are numbered from the start of iOS to iOS11 and beyond.
The iOS operating system is highly popular among its users, the system is relatively simple and quick as well. Unlike the closed source operating system, Apple offers the possibility to develop content or applications for iOS. These applications makes the iOS operating system even more enjoyable, think of apps for managing your calendars, mail, and time. Of course there are also applications available for recreational use in the form of games.
Developing applications for iOS is made possible in an environment released specifically by Apple. These Software Development Kits are available for the different versions of iOS and are freely accessible on Apple's domains. These SDKs can be downloaded and used by anyone.
Apps for iOS/Apple are constantly updated to protect against data- or security vulnerabilities. Another reason is to improve the user-friendliness of the app, think about the layout of the interface and/or bug detection which are then removed. The latest version of the iOS application can be found in Apple's App Store.