NoSQL databases are a type of database management system that do not use the traditional relational database model. Instead, they use a variety of data models, such as document, key-value, graph, or column-family. NoSQL databases are designed to handle large volumes of unstructured or semi-structured data, making them ideal for big data applications. They are also highly scalable and can handle high levels of traffic and data throughput. NoSQL databases are often used in web applications, mobile apps, and IoT devices. They are also popular in cloud computing environments, where they can be easily deployed and managed.