Learn in the textbookRepresentative Types of Operating Systems
DefinitioniOS is the mobile OS that Apple develops for its own iPhone smartphones.
ExplanationIt was designed around touch operation, where you control the screen with your fingers, and apps are, as a rule, obtained from Apple's App Store. It ships only on Apple devices, and its source code is not public. Its core comes from the same design as Mac OS, and the version for the iPad is now called iPadOS.
AnalogyIt is like a shopping mall where one company manages both the building and the floor space, and only shops that pass its review can move in.
Memory hookIt started out as iPhone OS and was later renamed iOS, keeping the "i" from iPhone.