What is a data structure node class?

A node class is a class that,
– relies on the base class for services and implementation, provides a wider interface to users than its base class,
– relies primarily on virtual functions in its public interface depends on all its direct and indirect base class can be understood only in the context of the base class can be used as base for further derivation can be used to create objects.

A node class is a class that has added new services or functionality beyond the services inherited from its base class.