This document discusses virtual functions, dynamic binding, pure virtual functions, and abstract classes in C++. Some key points: - Virtual functions allow derived classes to override base class functions. The decision of which function to call is made at runtime. - Dynamic binding occurs at runtime and chooses the function to call based on the actual object type. It requires pass by reference. - A pure virtual function is a virtual function with no implementation in the base class, forcing derived classes to override it. - An abstract base class contains at least one pure virtual function and cannot be instantiated directly, only derived from. Abstract classes define common interfaces for derived classes.