In this code, the Shape class is an abstract class because it has a pure virtual function draw(). This means that the Shape class cannot be instantiated directly and must be subclassed to provide an implementation for the draw() function. 

To create a subclass of an abstract class in C++, you must provide an implementation for all of the pure virtual functions of the base class. Here's an example: 

By using the abstract term to describe classes with pure virtual functions in C++, you can clearly indicate to other developers that the class is not meant to be instantiated directly and must be subclassed to provide an implementation.