How does polymorphism help in loose coupling?

Short answer: Code depends on interfaces or base classes, not concrete implementations. Makes system flexible, extendable, and easier to maintain. void StartVehicle(Vehicle v) { v.Start(); } // Works with any derived type

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.