The '.xcodeproj' file extension, though technically a directory bundle (or package) on macOS, represents an Xcode project. It is the fundamental organizational unit for developing applications, frameworks, and libraries using Apple's integrated development environment (IDE), Xcode. An '.xcodeproj' bundle contains all the necessary information for Xcode to understand, build, and manage a software project targeting Apple platforms such as iOS, macOS, watchOS, and tvOS. This includes references to source code files (like Swift, Objective-C, C++, etc.), user interface files (e.g., Storyboards, XIBs, SwiftUI views), asset catalogs, build settings, compiler flags, linker settings, project configurations, targets (which define what to build, e.g., an app, a framework, a test bundle), and schemes (which define how to build and run a target). The core of an '.xcodeproj' is the 'project.pbxproj' file, a property list that stores the project's structure and settings. While it appears as a single file in Finder, it's a folder containing multiple files and subdirectories. It is not meant to be opened or edited manually by users, but rather managed exclusively by the Xcode IDE.