SQL (Structured Query Language) is a standard language for managing and manipulating relational databases. A relational database is a type of database that stores data in the form of tables, with rows representing individual records and columns representing specific data points (attributes) within each record. SQL is used to create, modify, and query these tables, as well as to control access to the data stored in them. Some popular examples of SQL-based databases include MySQL, Oracle, and Microsoft SQL Server.