What is the difference between an abstract method and a virtual method?

Short answer: Feature Abstract Method Virtual Method Implementatio No implementation Has implementation Must override? Must be overridden Optional to override Class type Must be in abstract class Can be in any class Purpose Force derived classes to implement Allow derived class to optionally override

Real-world example (ShopNest)

ShopNest has a base PaymentMethod with virtual decimal Fee(). UpiPayment and CardPayment override the fee logic without changing the checkout caller.

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.