The iOS Simulator is a software application that allows developers to run and test their iOS apps on a computer without needing a physical iPhone or iPad. It mimics the hardware and software environment of these devices, enabling developers to see how their apps will perform on different screen sizes and operating system versions. By using the iOS Simulator, developers can quickly identify and fix issues in their apps, making the development process more efficient. It is part of the Xcode development environment, which is essential for creating apps for the Apple ecosystem.