what is deligate in asp.net code example

Example: delegate c# mvc

using System;
namespace MVC
{
    public class Book
    {
        // declare a delegate for the bookpricechanged event
        public delegate void BookPriceChangedHandler(objectsender,
        BookPriceChangedEventArgs e);
        
        // declare the bookpricechanged event using the bookpricechangeddelegate
        public event BookPriceChangedHandlerBookPriceChanged;
        
        // instance variable for book price
        object _bookPrice;
        
        // property for book price
        public object BookPrice
        {
            set
            {
                // set the instance variable
                _bookPrice=value;
                
                // the price changed so fire the event!
                OnBookPriceChanged();
            }
        }
        
        // method to fire price canged event delegate with proper name
        // this is the method our observers should be implenting!
        protected void OnBookPriceChanged()
        {
            BookPriceChanged(this, new BookPriceChangedEventArgs(_bookPrice));
        }
    }
}