MongoDB is an open-source document database engine that offers excellent performance and scalability. Document databases such as MongoDB dispense with the complex schemas of traditional relational databases, sacrificing referential integrity for performance, scalability, and ease of development.
There are no tables, rows, or fields in MongoDB, only documents. They have indexes, but these documents are independent of each other and contain all the necessary information about the object they represent.
Express is a framework for node.js applications that contains countless methods, utilities, and middleware, in general, to make our development more stable and faster. It is very important to achieve the correct functioning of the final application.
Angular is another framework, this time dedicated to the part of the client that allows you to create single-page applications, that is, applications that do not need to reload the page. The simplicity it brings to the programmer is that it organizes the code in layers, thus avoiding endless lines of code. This is a project currently maintained by Google, open source, and in full swing.
Now you know what MEAN is and what its main features are.