What is the meaning of no sql database?

Answer 1

A no sql database is a database that doesn't require only SQL for its manipulation. For instance, some mo sql databases allow you to store data expressed in JSON format.

Answer 2

Its Not Only SQL. NoSQL databases doesn't follow fixed schema. Its schema is very dynamic that it can be changed at anytime. Data is tored in the form of JSON
Few types of NoSQL databases
Graph Database- Neo4J
Document Database- MongoDB, CouchDB
Key-Value store Database- Redis
Columnar Database- HBase, Cassandra