What is the difference between an abstract class and a normal class?

Short answer: Feature Abstract Class Normal Class Instantiation Cannot instantiate Can instantiate Methods Can have abstract methods All methods must have implementation Purpose Serve as base for inheritance General purpose use

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.