TypeScript is a superset of JavaScript that adds static typing to the language, allowing developers to catch errors early during development. It extends JavaScript by enabling the use of type annotations, interfaces, and classes, providing better tooling, code clarity, and maintainability. TypeScript code is compiled to standard JavaScript, making it compatible with any browser or JavaScript environment. It is particularly useful for large-scale applications and improves the development experience with features like autocompletion, refactoring support, and enhanced error checking.