Concrete Observer (NewsSubscriber):?

Short answer: The NewsSubscriber class represents an observer. Each subscriber has a name and implements the Update() method to receive news updates from the publisher. public class NewsSubscriber : IObserver

Example code

{
private readonly string _name;
public NewsSubscriber(string name) => _name = name;
public void Update(string news) => Console.WriteLine($"{_name} received news: {news}"); }

Real-world example (ShopNest)

When order status changes, observers update email, SMS, and analytics without the Order class knowing each one.

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.