From Wikipedia..."SQL Structured Query Language is a special-purpose programming language designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS)."

From Ross...SQL is used to access, manipulate and manage the database portion of an application. Reguardless of what RDBMS is being SQL is used by the application to interact with it although syntax and form tends to vary slightly between different RDBMSs.