The MEAN stack is a software stack—that is, a set of the technology layers that make up a modern application—that’s built entirely in JavaScript. MEAN represents the arrival of JavaScript as a “full-stack development” language, running everything in an application from front end to back end. Each of the initials in MEAN stands for a component in the stack:

MongoDB: A database server that is queried using JSON (JavaScript Object Notation) and that stores data structures in a binary JSON format

Express: A server-side JavaScript framework

Angular: A client-side JavaScript framework

Node.js: A JavaScript runtime

A big part of MEAN’s appeal is the consistency that comes from the fact that it’s JavaScript through and through. Life is simpler for developers because every component of the application—from the objects in the database to the client-side code—is written in the same language. 

This consistency stands in contrast to the hodgepodge of LAMP, the longtime staple of web application developers. Like MEAN, LAMP is an acronym for the components used in the stack—Linux, the Apache HTTP Server, MySQL, and either PHP, Perl, or Python. Each piece of the stack has little in common with any other piece. 

This isn’t to say the LAMP stack is inferior. It’s still widely used, and each element in the stack still benefits from an active development community. But the conceptual consistency that MEAN provides is a boon. If you use the same language, and many of the same language concepts, at all levels of the stack, it becomes easier for a developer to master the whole stack at once.

Most MEAN stacks feature all four of the components—the database, the front end, the back end, and the execution engine. This doesn’t mean the stack consists of only these elements, but they form the core.