CoffeeScript is a little language that compiles into JavaScript. Underneath all of those embarrassing braces and semicolons, JavaScript has always had a gorgeous object model at its heart. CoffeeScript is an attempt to expose the good parts of JavaScript in a simple way.
CoffeeScript is an alternative syntax for JavaScript. Unlike other languages that compile to JavaScript, it deliberately retains the exact semantics of JavaScript. Furthermore, it provides syntax help to enable you to write correct, verbose, JS code concisely.