What does SQL mean?

SQL = Structured Query Language.

SQL is a specialized programming language for sending queries to databases. Most industrial-strength and many smaller database applications can be controlled using SQL. Each specific application will have its own version of SQL implementing features unique to that application, but all SQL-capable databases support a common subset of SQL.
Many dbms (database management systems) allow stored procedures add control structures and variables to the data retrieval/ modification statements. Stored procedures are compiled and executed faster.