What is a concrete class?
A class that is neither derived from another class nor is meant to serve as the base for other classes is a concrete class. Concrete classes have no virtual member functions or protected members.
They are widely used in object-based languages (such as Ada83). However, even in object oriented languages such as C++, they are still useful: string, complex, and vector are examples of concrete classes in C++. The opposite of a concrete class is an abstract class.