NoSQL is a blanket term used to describe nontraditional methods of storing data in a database. The vast majority of NoSQL databases are not relational—unlike RDBMS—which means that they normally cannot perform operations such as JOIN. There are a number of other features that distinguish an SQL database from a NoSQL database. With a NoSQL database, we have the ability to not impose a fixed schema—for example, a collection on MongoDB can hold different fields, and so they can accept any kind of document. With NoSQL you can (and should) take advantage of denormalization, making a tradeoff between storage and speed.

Modern NoSQL databases include key-value stores, document stores, column family stores, and graph databases.