MERN MERN stack is a web development framework. It consists of MongoDB, ExpressJS, ReactJS, and NodeJS as its working components. Here are the details of what each of these components is used for in developing a web application when using MERN stack:

MongoDB: A document-oriented, No-SQL database used to store the application data.

ExpressJS: A framework layered on top of NodeJS, used to build the backend of a site using NodeJS functions and structures. Since NodeJS was not developed to make websites but rather run JavaScript on a machine, ExpressJS was developed.

ReactJS: A library created by Facebook. It is used to build UI components that create the user interface of the single page web application.

MERN Stack is one of the most popular user-friendly Full Stack Web Development structures. It helps us improve our applications to a great extent. You don't need to learn multiple programming languages for web application development because MERN stack covers both front-end as well as back-end. It will give you the advantage of using a single language i.e. JavaScript, for web development which makes it very effective and powerful.