Structured Query Language (SQL):
The Structured Query Language (SQL) is the set of instructions used to interact with a relational database. In fact, SQL is the only language that most databases actually understand. Whenever you interact with such a database, the software translates your commands (whether they are mouse clicks or form entries) into SQL statement that the database knows how to interpret. SQL has three major components: the Data Manipulation Language (DML), the Data Definition Language (DDL), and the Data Control Language (DCL).
For more on SQL:
For SQL Tutorial: http://www.w3schools.com/sql/sql_intro.asp