Swift is a powerful, open-source programming language developed by Apple for building applications on iOS, macOS, watchOS, and tvOS. It is designed to be easy to use, with a clean and expressive syntax, while offering high performance and modern features like optionals, type inference, and memory safety. Swift combines the best of both high-level and low-level programming, making it suitable for a wide range of applications, from mobile apps to system software. It is intended to be more efficient and safer than its predecessor, Objective-C, and is widely adopted for developing modern Apple ecosystem applications.