MERN Stack is a JavaScript-based tech stack that makes web development and deployment easier. MERN refers to four technologies: MongoDB, Express.js, React.js, and Node.js. They form a stack where MongoDB is used as a cross-platform document-oriented database for JSON-like storage, such as indexing, ad-hoc queries, replication, and load balancing.
Express is a backend framework used for developing web applications and APIs. React is a frontend library for creating a seamless user interface, and Node is a backend JS runtime environment, allowing developers to run code outside of a browser.