PL/SQL means Procedural Language/Structured Query Language. It is an extension to the standard SQL that was created by Oracle, (with a syntax and structure similar to Ada). The language also includes such object oriented programming techniques such as encapsulation, function overloading, and information hiding.
The PL/SQL compiler and interpreter are embedded in Oracle Developer. This provides a server side, procedural language that is nicely integrated with SQL. PL/SQL stored procedures can also be called from most other Oracle clients, including Oracle Call Interface and Oracle Forms.
The PL/SQL platform is best used in an Enterprise setting. Providing good performance for even the most complex Oracle installations.