MongoDB is opensource document-oriented DB.
MongoDB is opensource document-oriented DB, and stores data in JSON like documents. It is highly flexible and scalable. It is used as an alternative of traditional SQL databases where data is stored in form of tables. NoSQL DBs are quite useful when the data is distributed, and useful when your data does not has fixed or frequently changing structure. Unlike tradition DBs the data is stored in form of collections and documents rather than tables and rows.