Microsoft SQL Server is a relational database management system (RDBMS) developed by Microsoft. It is used to store and manage data, allowing users to query, insert, update, and delete data through SQL (Structured Query Language). SQL Server is known for its scalability, security features, and integration with other Microsoft products like Azure, Power BI, and Visual Studio. It supports advanced features like transactions, data encryption, backup and recovery, and high availability. Microsoft SQL Server is widely used in enterprise environments for managing large volumes of data and running mission-critical applications.