MongoDB is an open-source database management system (DBMS) that uses a document-oriented database model which supports various forms of data. It is one of the numerous nonrelational database technologies which arose in the mid-2000s under the NoSQL banner for use in big data applications and other processing jobs involving data that doesn't fit well in a rigid relational model. Instead of using tables and rows as in relational databases, the MongoDB architecture is made up of collections and documents.
Documents, which also must incorporate a primary key as a unique identifier, are the basic unit of data in MongoDB. Collections contain sets of documents and function as the equivalent of relational database tables. Collections can contain any type of data, but the restriction is the data in a collection cannot be spread across different databases.
The BSON document storage and data interchange format used in MongoDB provides a binary representation of JSON-like documents. Automatic sharding is another key feature that enables data in a MongoDB collection to be distributed across multiple systems for horizontal scalability as data volumes and throughput requirements increase.
The NoSQL DBMS uses a single master architecture for data consistency, with secondary databases which maintain copies of the primary database. Operations are automatically replicated to those secondary databases for automatic failover.