NoSQL databases are a type of database designed to handle large volumes of unstructured or semi-structured data. Unlike traditional relational databases, which use tables and fixed schemas, NoSQL databases offer more flexibility in how data is stored and accessed. This makes them ideal for applications that require rapid scaling and can accommodate various data formats, such as JSON or XML. There are several types of NoSQL databases, including document stores, key-value stores, column-family stores, and graph databases. Each type is optimized for specific use cases, such as managing user profiles, storing session data, or analyzing social networks. This versatility allows developers to choose the best database solution for their application's needs.