The document introduces the MEAN stack, which is an open source full-stack JavaScript platform that includes MongoDB, Express, AngularJS, and Node.js. It is used to build dynamic web applications and single page applications. The MEAN stack uses MongoDB for the database, Express for the backend server framework, AngularJS for the frontend framework, and Node.js as the runtime environment. It is a JavaScript-based alternative to traditional server-rendered technologies like LAMP stacks.