About a Database Database is a physical container of collections. Each database gets its own set of files in a file system. A single MongoDB server typically has multiple databases. MongoDB - An overview MongoDB is an open source, cross-platform, and document oriented database that provides high performance, high availability, and easy scalability in the realm of NoSQL databases. MongoDB works on the concept of collection and documents. Collection Collection is a group of MongoDB documents. It is the equivalent of tables in RDBMS. A collection exists within a single database. Collections do not enforce a schema. Documents within a collection can have different fields. Typically, all documents in a collection are for similar or related purposes. Documents A document is a set of key-value pairs. Documents have dynamic schema, which means that documents in the same collection do not need to have the same set of fields or structure, and common fields in a collection's documents may hold different types of data. The following table shows the relationship of RDBMS terminology with MongoDB.