Is Keyword in C#

Is keyword is used to check variable's type ...

using System;

using System.Collections;

namespace IsKeyword

{

    class A

    {

        public string str = "A";

    }

    class B

    {

        public string str = "B";

    }

    class Program

    {

        static void Main()

        {

            ArrayList al = new ArrayList();

            al.Add(new B());

            al.Add(new A());

            al.Add(new B());

            al.Add(new B());

            al.Add(new A());

            al.Add(new A());

            al.Add(new B());

            foreach (var item in al)

            {

                if (item is A)

                {

                    Console.WriteLine(((A)item).str);

                }

            }

            Console.ReadKey();

        }

    }

}