MERN is a collection of open-source technologies that developers use to build web and mobile applications.

MERN stands for

• MongoDB
• Express
• React
• Node

MERN is a full stack approach, this means it includes the front-end (client) and the back-end (server) components.  MERN uses javascript.

• Express.js and MongoDB are used for the back-end.
• React is used for the front-end, its a a JavaScript library for developing User Interfaces (UIs)