An SDK, or Software Development Kit, is a collection of tools, libraries, and documentation that developers use to create applications for specific platforms or frameworks. It simplifies the development process by providing pre-built functions and components, allowing developers to focus on building unique features rather than starting from scratch. SDKs often include APIs, sample code, and debugging tools, making it easier to integrate with other software or services. They are commonly used for mobile app development, web applications, and game development, enabling developers to leverage existing technologies and enhance their projects efficiently.