History. "NoSQL" originated from a twitter hashtag #nosql, meaning non SQL, a counter-approach to the relational databases. As time passed, it has more meanings and people have re-invented a new name for it, "not only SQL".
NoSQL emerged at a time that relational databases has dominated the storing world. It seemed, during the time, the relational database was the only way to persist a large amount of data. However, as the volume kept growing, despite of the use of partioning, the relational database began to reach its limitation. People needs a new solution that can handle extreme large data volumes on a cluster of commodity servers A number of NoSQL databases were invented to achieve this goal, such as MongoDB, Cassandra, CouchDB, Riak, etc.