What is AsyncronousController and Async and await key word in mvc 4.5

Async and await are markers which marked code positions from where control should resumed after a task (thread) completes.It is introduced in .net 4.5 framework.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace AsyncANDAwait
{
    class Program
    {
        static void Main(string[] args)
        {
            Method();
            Console.WriteLine("Main Method called");
            Console.ReadLine();
        }

        static async void  Method()
        {
           await Task.Run(new Action(LongTaskMethod));
           Console.WriteLine("AsyncMethod called"); //wait until long task finished.
        }
        static void LongTaskMethod()
        {
            Thread.Sleep(20000);
        }
    }
}