In simple terms, a Restful API Description Language is a type of computer code that helps developers create applications that can communicate with other applications. This code helps the applications "talk" to each other to share information and provide instructions. The language is similar to other computer programming languages, but it is specifically designed for applications to use when exchanging information. By using this language, developers can build applications that can communicate quickly and accurately with each other, making it easier to create complex data exchanges that wouldn't be possible with any other type of language.