What is the role of interfaces in achieving polymorphism?

Short answer: Interfaces allow different classes to implement the same contract, enabling dynamic behavior at runtime. interface IDriveable { void Drive(); } class Car : IDriveable { public void Drive() => Console.WriteLine("Car drives"); } class Bike : IDriveable { public void Drive() => Console.WriteLine("Bike drives"); }

Example code

Interfaces allow different classes to implement the same contract, enabling dynamic behavior at runtime. interface IDriveable { void Drive(); }
class Car : IDriveable { public void Drive() => Console.WriteLine("Car drives"); } class Bike : IDriveable { public void Drive() => Console.WriteLine("Bike drives"); }

Real-world example (ShopNest)

Checkout calls IPaymentGateway.Charge(). Razorpay and Stripe adapters implement the same interface, so ShopNest can switch gateways without rewriting the order service.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.