The MEAN stack is a collection of technologies used to build full-stack web applications. Its components include: MongoDB, a NoSQL database that stores data as JSON documents; Express.js, a web framework for Node.js that simplifies the development of web applications and APIs; AngularJS, a JavaScript framework developed by Google to create interactive user interfaces and single-page web applications (SPAs) following the MVC (Model-View-Controller) pattern; and Node.js, a server-side JavaScript runtime environment known for its ability to handle multiple simultaneous connections and its efficiency in processing requests.