Jdbc API contains a set of classes and Interfaces where classes definition is provided by Sun Micro System and Interfaces Implementation are not provided. For interface Implementation classes will be provided by vendors, these set of classes are called Jdbc Driver Software.
A Driver software contains set of classes among these classes one class is driver class.
Driver class is a mediator class between a java application and a database.
Java Application use Jdbc API and this API connect to driver class, then driver class connect to database.