T-SQL, or Transact-SQL, is an extension of SQL (Structured Query Language) used primarily with Microsoft SQL Server. It adds additional features to standard SQL, such as procedural programming, local variables, and support for error handling, making it more powerful for database management and manipulation. T-SQL allows users to write complex queries and scripts to interact with databases. It is commonly used for tasks like retrieving data, updating records, and managing database structures. By leveraging T-SQL, developers can create efficient and scalable applications that rely on SQL Server for data storage and retrieval.