What is polymorphism in OOP?

The simple meaning

The word polymorphism comes from many forms. In code it means you can use a single method name and the program decides which actual behaviour to run based on the object involved. This keeps your code clean and open to new types.

Compile time polymorphism

This is achieved with method overloading. Several methods share a name but take different parameters, and the compiler picks the right one before the program runs.

int area(int side) { return side * side; }
int area(int l, int b) { return l * b; }

int area(int side) { return side * side; }
int area(int l, int b) { return l * b; }

# Python has no compile time overloading.
# A default argument covers both cases.
def area(l, b=None):
    return l * l if b is None else l * b

Run time polymorphism

This is achieved with method overriding. A parent reference can point to a child object, and the child version of the method runs at run time. This is the powerful form used in real designs.

class Shape {
public:
    virtual void draw() { cout << "drawing shape"; }
};
class Circle : public Shape {
public:
    void draw() override { cout << "drawing circle"; }
};

Shape* s = new Circle();
s->draw();   // prints drawing circle

class Shape {
    void draw() { System.out.println("drawing shape"); }
}
class Circle extends Shape {
    @Override
    void draw() { System.out.println("drawing circle"); }
}

Shape s = new Circle();
s.draw();   // prints drawing circle

class Shape:
    def draw(self):
        print("drawing shape")
class Circle(Shape):
    def draw(self):        # override
        print("drawing circle")

s = Circle()
s.draw()   # prints drawing circle

Why it matters

Polymorphism lets you write code against a general type like Shape and add new shapes later without touching the old code. This is the foundation of flexible and extendable software.