- MongoDB is a document-oriented, non-relational database that uses JSON-like documents with dynamic schemas, horizontal scaling with sharding and replication, and high performance. - It is used by many large companies and is a good fit for huge, unstructured data or when dynamic schemas are needed. However, it does not support transactions or have the same data integrity features as relational databases. - MongoDB can store data in flexible document formats, allows ad hoc queries, and supports common operations like insert, update, delete. Features include replication, sharding, indexing, geospatial queries and MapReduce.