NoSQL is a non-relational database management systems which is different from traditional relational database management systems in some significant ways.
It is designed for distributed data stores where large scale of data storing needs don't require fixed schema, avoid join operations and typically scale horizontally.
It was coined by Carlo Strozzi in the year 1998. He used this term which did not have an SQL interface like Open Source, Light Weight, and DataBase. In early 2009, Eric Evans a Rackspace employee reused the term to refer databases that does not conform to atomicity, consistency, isolation, durability which are the four features of traditional relational database systems. The "no.sql(east)" conference held in Atlanta, USA wherein NoSQL was discussed and debated until the term got a momentum and saw unprecedented growth.