Complex sentence: Apps provide a specific set of functions which, by definition, do not include the running of the computer itself.operating system (such as iOS, macOS, Windows, or Android).
Split into simpler sentences: Apps provide a specific set of functions which, by definition, do not include the running of the computer itself. Apps are designed to run on specific devices, and are written for a specific operating system (such as iOS, macOS, Windows, or Android).