TypeScript is a typed superset of JavaScript that compiles to plain JavaScript and allows for large-scale application development. It adds features like classes, modules, interfaces, and optional static typing to JavaScript. TypeScript compiles to plain JavaScript, so it can be used anywhere JavaScript runs in browsers, hosts, and operating systems. It supports using existing JavaScript and third-party libraries while also providing benefits like cleaner code and catching errors for Angular, jQuery, and library developers working on larger applications.