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What is a delegate in C#, and how does it enable passing methods as values? What is a closure and what is a common pitfall? How do events differ from plain delegates? What is an event, and how does it differ from a plain public delegate field? How does variable capture (closures) work in a C# lambda expression, and what pitfall occurs when capturing a loop variable? What causes event-handler memory leaks and how do you prevent them? What is the difference between multicast delegate invocation and exception handling? How do the built-in Func<>, Action<>, and Predicate<T> generic delegate types differ, and when would you use each? How would you implement the 'weak event pattern' to prevent event subscribers from causing a memory leak by keeping the publisher alive indefinitely? How does a lambda expression get compiled differently when it captures NO outer variables versus when it DOES capture outer state?
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What are multicast delegates, and in what order do their subscribed methods get invoked?

Intermediate

Answer

A delegate can hold references to MULTIPLE methods simultaneously (added via +=), forming an invocation LIST — calling the delegate invokes every subscribed method IN THE ORDER they were added, one after another, sequentially on the same thread.
Action greetings = null;
greetings += () => Console.WriteLine("Hello");
greetings += () => Console.WriteLine("Hi");
greetings += () => Console.WriteLine("Hey");
greetings?.Invoke(); // prints Hello, Hi, Hey in that order
Real-world example Allowing multiple independent parts of an application to subscribe to and react to the same event, like a logging system and a UI update both reacting to OnDataChanged.

Common follow-ups: What happens to the RETURN VALUE if a multicast delegate has a non-void return type and multiple subscribers?

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All 17 Delegates, Events & Lambdas questions