What is Is & as keyword in C#

Is Keyword is used to check the type while As is used for type casting.

Exp-

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

namespace IsAndAsKeyword
{
    class Program
    {
        static void Main(string[] args)
        {
            object obj = "this is a test";

            //check Is keyword
            if (obj is string)
            {
                Console.WriteLine("obj is {0} type.", "string");
            }
            else
            {
                Console.WriteLine("obj is not {0} type.", "string");
            }

         
            //check As keyword
            var a = obj as string;
            if (a is string)
            {
                Console.WriteLine("obj as {0} type.", "string");
            }
            else
            {
                Console.WriteLine("obj as not {0} type.", "string");
            }

            Console.ReadLine();
        }
    }
}