A Property List (plist) is a flexible and convenient format for storing application data, primarily used in macOS, iOS, and other Apple operating systems. Originally developed by NeXT and later adopted by Apple, plist files are essentially structured data stores that use a key-value pair system. They are most commonly used to store user preferences, configuration settings, and information about installed applications, such as the Info.plist file found in every app bundle. Plist files can exist in several formats: XML, binary, or the older OpenStep ASCII format. The XML version is human-readable and follows a specific Document Type Definition (DTD), while the binary version is optimized for performance and smaller file sizes, though it requires specialized tools to read. Developers use these files to manage global settings, localizations, and hardware configurations, making them a cornerstone of the Apple ecosystem's software architecture and application lifecycle management. Because they support nested arrays and dictionaries, they are highly effective for representing complex hierarchical data structures in a way that is easily parsed by system APIs.