What is SQL?

Is SQL is a language or not? 

SQL is not a language.So i will  tell you that what is Sql in actual.

SQL and RDBMS:

The history of marriage of SQL to the relational model is primarily due to the fact that the technology and language were developed side-by-side in the 1970s by E.F. Codd, Donald D. Charmberlin and Raymond F.
Relational model is widely used nowdays and SQL is the most common way to deal with RDBMS.

If not a language, then what is SQL? 

SQL standard is more like a protocol or a series of gernally accepted statements based on mathematical principles of set theory, predicate logic and relational algebra.

RDBMS developers implement these standards vary significantly across various proprietary software enough so to almost classify each individual implementation as a language of its own. 

SQL can be called as software based language as multiple companies follow different syntax/rules of writing SQL. 

Most vendors of SQL:

Each company implements their own unique functions,database engine(in some cases) procedural languages on top of the traditional ANSI SQL standard  statements.

Sometimes, companies choose to abandon the standard at times in favor of their own personal information.