Instantiating a Derived from a Base

Hi,

I was learning about RTTI when I ran across this example. This line,
out of the example, confused me. It is declaring a pointer to a base
type and instantiating it with a derived class. I can say the
words ... yet I don't get it. What do I have, a base or a derived? Can
anyone push me in the right direction.

  abc *abc_pointer = new xyz();

/*
-------------------------------------------------------------------------------------------------
*/

#include <iostream>

class abc // base class
{
public:
  virtual void hello()
  {
    std::cout << "in abc";
  }
};

class xyz : public abc
{
  public:
  void hello()
  {
    std::cout << "in xyz";
  }
};

int main()
{
  abc *abc_pointer = new xyz();
  xyz *xyz_pointer;

  // to find whether abc is pointing to xyz type of object
  xyz_pointer = dynamic_cast<xyz*>(abc_pointer);

  if (xyz_pointer != NULL)
    std::cout << "abc pointer is pointing to a xyz class object"; //
identified
  else
    std::cout << "abc pointer is NOT pointing to a xyz class object";

  return 0;
}