MEAN / MERN is a collection of JavaScript-based technologies. In MEAN Stack we use MongoDB, Express.js, Angular, and Node.js, and in MERN Stack we use MongoDB, Express.js, React JS, and Node.js to develop web applications. MongoDB is a free and open-source cross-platform document-oriented database program. Classified as a NoSQL database program, MongoDB uses JSON-like documents with schemas. Express is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. Angular is a TypeScript-based open-source front-end web application framework developed by Google. React is an open-source, front end, JavaScript library for building user interfaces or UI components. It is developed and maintained by Facebook. Node.js is an open-source, cross-platform JavaScript run-time environment that executes JavaScript code server-side.