This document provides an introduction to NoSQL databases. It discusses that NoSQL refers to non-relational databases that are not based on SQL and are focused on scalability. Some common types of NoSQL databases include column stores, key-value stores, document stores, graph databases, and XML databases. NoSQL databases are designed to handle large volumes of data across many servers and provide high availability with no single point of failure. Common uses of NoSQL databases include distributed systems like social networks where data is highly distributed and needs to be replicated across servers.