NoSQL databases were created to handle large and growing datasets for web applications. They are non-tabular, distributed, open source, and designed for high performance, scalability, and availability. The document focuses on key characteristics of NoSQL like schema flexibility, horizontal scaling, and the BASE consistency model. It also covers major NoSQL types (key-value, document, and column-oriented), queries, and compares NoSQL to SQL databases in terms of features, performance, and cost.