What is Swift and what are its key features?

Swift is a powerful programming language developed by Apple for iOS, macOS, watchOS, and tvOS development. Key features: 1) Type safety - prevents type-related errors, 2) Optionals - handle absence of values safely, 3) Automatic Reference Counting (ARC) - memory management, 4) Closures - self-contained blocks of functionality, 5) Generics - write flexible, reusable code, 6) Protocol-oriented programming, 7) Fast performance, 8) Modern syntax.