C#でのデリゲートとは？

    public static class Delegate
    {
        public delegate string GetHelloDelegate(string str);    public delegate void SayHelloDelegate();
 
    public static void Say()
    {
        var func = new SayHelloDelegate(() => Console.WriteLine("Hello World"));
        func();
    }
 
    public static void Say2()
    {
        var func = new GetHelloDelegate(str => $@"Hello {str}");
        Console.WriteLine(func("CSharp"));
    }
}