what is polymorphism?

have at look at these
http://www.codeproject.com/KB/architecture/OOP_Concepts_and_manymore.aspx#Polymorphism[^]
Introduction to Polymorphism in C++[^]
Polymorphism[^]

And few more:
- http://www.dreamincode.net/forums/topic/9872-polymorphism-tutorial/[^]
- http://www.cs.bu.edu/teaching/cpp/polymorphism/intro/[^]

Polimorphism is one of the fundamental pillars of Object Oriented Programming. You can't hope to learn it from a 'quick answer'. Buy a (good) OOP book and study it.

polymorphism in the context of object-oriented programming, is the ability to create a variable, a function, or an object that has more than one form.

Polymorphism is not the same as method overloading or method overriding.[1] Polymorphism is only concerned with the application of specific implementations to an interface or a more generic base class. Method overloading refers to methods that have the same name but different signatures inside the same class. Method overriding is where a subclass replaces the implementation of one or more of its parent's methods. Neither method overloading nor method overriding are by themselves implementations of polymorphism.[2]

Please have a look in the following program.
Just have it compiled and debug. you will see the wonderful nature or polymorphism.
if you dont understand revert back will explain..

source - wikipedia

#include <iostream>
#include <string>
 
using namespace std;
 
class Animal {
public:
        Animal(const string& name) : name(name) {}
        virtual string talk() = 0;
        const string name;
};
 
class Cat : public Animal {
public:
        Cat(const string& name) : Animal(name) {}
        virtual string talk() { return "Meow!"; }
};
 
class Dog : public Animal {
public:
        Dog(const string& name) : Animal(name) {}
        virtual string talk() { return "Woof! Woof!"; }
};
 
// prints the following:
//
// Missy: Meow!
// Mr. Mistoffelees: Meow!
// Lassie: Woof! Woof!!
//
int main() {
        Animal* animals[] = {
                new Cat("Missy"),
                new Cat("Mr. Mistoffelees"),
                new Dog("Lassie")
        };
 
        for (int i = 0; i < 3; ++i) {
                cout << animals[i]->name << ": " << animals[i]->talk() << endl;
                delete animals[i];
        }
}
</string></iostream>

It[^] could be also designed :) :

class Animal : public Individual
{
 //..
public:
 virtual LPCTSTR SayHello() = 0;
 //..
};

class Cow : public Animal
{
  //..
public:
  virtual LPCTSTR SayHello() { return _T("Muh"); };
  //..
};

class Dog : public Animal
{
  //..
public:
  virtual LPCTSTR SayHello() { return _T("Wow"); };
  //..
};

void test(Covey& covey)
{
  POSITION pos(covey.GetFirstPosition());
  while (pos) {
    Animal* pAnimal(covey.GetNext(pos));
    if (pAnimal) {
      pAnimal->SayHello(); // anybody can it in its own way
    }
  }
}