What is MongoDB?
A document-oriented NoSQL database that stores records as flexible, JSON-like BSON documents.
Definition
MongoDB stores data as BSON documents in collections, with no enforced table schema, so records in one collection can carry different fields—useful when a data model is still moving, and a liability when nobody writes down what the shape actually is. Its design favors embedding related data in a single document over normalizing across joins, which turns a common read into one lookup instead of several. The aggregation pipeline handles grouping and transformation, and sharding distributes collections across a cluster by shard key, which is the single most consequential choice for a large deployment. Since version 4.0 it supports multi-document ACID transactions, closing the durability gap with relational databases. Mongoose is the standard ODM for Node.js applications, adding the schema layer back at the application level.