NoSQL systems 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 flexibility in data storage and retrieval. They can efficiently manage diverse data types, making them suitable for applications like big data analytics and real-time web applications. These systems come in various types, including document stores, key-value stores, column-family stores, and graph databases. Each type is optimized for specific use cases, allowing developers to choose the best fit for their needs. This versatility has made NoSQL increasingly popular in modern software development.