What do you mean by NOSQL database?

NoSQL is a class of database management system (DBMS) that do not follow all the rules of a relational DBMS and cannot use traditional SQL to query data. The term is somewhat misleading when interpreted as :No SQL" and most translate it as "not only SQL" as this type of database is not generally a replacement but, rather a complementary addtion to RDBMSs and SQL.

NoSQL - based systems are typically used in ver large databaases, which are paricullary prone to performance problems caused by the limitations of SQL and relational model of databases. Many think of NoSQL as the modern database of choice that scales with web requirments. Some notable implementations of NoSQL are Facebook's Cassandra database, Google's Big Table and Amazon's Simple DB and Dynamo.

A NoSQL or Not Only SQL database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases.

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source: Wikioedia

That's means next generation database which address some below point's. This could contain huge amount of data.

• Non relational.
• Distributed.
• Open source.
• Scaleable.

This is what i know about nosql. There are lots of more characteristics of nosql.