what is dictionary in c#?

 Dictionary<int, string> obja = new Dictionary<int, string>();

            obja.Add(1, "DotNet");

            obja.Add(2, "Java");

            obja.Add(3, "Php");

            foreach(int k in obja.Keys)

            {

                Console.WriteLine(k);

            }

            foreach (string kk in obja.Values)

            {

                Console.WriteLine(kk);

            }

gowthaman8870226416