The .app extension on macOS signifies an Application Bundle. This isn't a single file, but rather a directory (presented as a single file in the Finder) that contains all the resources needed to run a specific application. Inside the bundle, you'll find the executable code, libraries, images, sounds, configuration files, and other assets required by the application. The structure of the bundle is standardized, allowing macOS to easily identify and launch the application. This structure also simplifies application management, as all the application's components are contained within a single, easily movable and deletable unit. Double-clicking a .app file launches the application it contains. The bundle structure also allows for easy localization, as different language resources can be stored within the bundle and selected based on the user's system settings. The Info.plist file within the bundle is crucial, as it contains metadata about the application, such as its name, version, icon, and the main executable file to run.