Originally Posted by http://www.objs.com/x3h7/cplus.htm
4. Polymorphism
C++ supports polymorphism by allowing member functions defined in classesto be overridden with member functions having the same names (operatoroverloading), but different implementations, in derived classes (subclasses).In selecting the appropriate member function to call in response to a functioninvocation, C++ distinguishes between the static type of a referenceand the dynamic type of the object it refers to at a given point. The dynamic type must be a descendant of the static type. The invocationis type-checked based on the static type of the reference. If the functioncalled is a virtual member function, the member function associated withthe actual object pointed to is called dynamically at run time. If thefunction is non-virtual, the call will have been statically bound to themember function of the reference's class at compile time.