Can abstract classes have non-abstract methods?

Short answer: Yes, abstract classes can have concrete methods with implementation. Allows shared behavior for derived classes. abstract class Animal {

Example code

public void Sleep() => Console.WriteLine("Sleeping");
public abstract void MakeSound();
}

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.