Oracle DBMS (DataBase Management System) is an enterprise grade database system designed to handle very large and complex databases with high availability and redundancy. Oracle databases are popular in ERP (Enterprise Resource Planning) systems such as Banner and PeopleSoft.
Oracle licenses are very complex due to its scalability and typical usage. Often the license is priced per processor, since the number of processors typically scales with the size of your database usage and operation. Large server clusters often have dozens of processors dedicated to processing request for an Oracle database.