MongoDB is a document oriented database, it is an open-source product and developed and suppored by company called 10gen. There are two types of licences available for mongo db General Public Licence and Commercial Licence.
It is scalable, document oriented and high performance database.
Document Oriented Database it means there is no SQL, database could be classified in to three types RDBS, (Relational Database Management System) OLAP (Online Analytical Processing) and NoSQL.
The main idea behind NoSQL database is horizontal scalability which was missing in relational database, horizontal scalabilities means you keep on adding more and more computers as you need more and more power.
NoSQL database is divided in to three types
1. Key Value Store