A function that is passed (by reference) to another 
function. The other function calls the callback function 
under defined conditions

one object to send message to other object is called 
callback and the Methos use to call back message are known 
as callback method.

hi Amit,

Thank you for giving Definition. Can you give some example?.

Thanks,
Geetha

Definition:
***********
Functions that are triggered when an associated event 
happens.

example 
*******

a) In C language function pointer is used as a callback 
functions.

b) In C++ virtual function are used as a callback function.

c) In c# delegate keyword is used to create a call back 
function.

example in c#
*************

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        public delegate int execute(int a, int 
b); //declare a delegate method

        static void Main(string[] args)
        {
            Program p = new Program();     
                  
            execute ex = new execute(p.add);
            Console.WriteLine(ex(2,3));  //add method is 
executed

            ex = new execute(p.subtract);
            Console.WriteLine(ex(2, 3)); //subtract method 
is executed            
        }

        public int add(int a, int b)
        {
            return (a + b);
        }

        public int subtract(int a, int b)
        {
            return (a - b);
        }
    }
}