Polymorphism means "many forms". It occurs when we have many classes that are related to each other by inheritance. It allows functions to operate on objects of different types through pointers/references of the base class.

Essential for implementing complex systems where behavior varies by specific type (e.g., a Shape interface where Circle and Square implement draw()).

• Virtual Call: $O(1)$ (plus a small overhead for vtable lookup).

cpp Standard
class Shape {
public:
    virtual void draw() { std::cout << "Drawing shape" << endl; }
};

class Circle : public Shape {
public:
    void draw() override { std::cout << "Drawing circle" << endl; }
};

int main() {
    Shape *s = new Circle();
    s->draw(); // Prints "Drawing circle"
}

• Slicing: Passing derived objects by value to functions taking base types, losing all derived data.
• Forgetting the virtual keyword in the base class.
• Not using virtual destructors.
• Forgetting to use override keyword (optional but helpful for catching errors).