PostBack is an event that is triggered when an action is performed by an ASP.Net Control. For example when we click on an asp button, the data on the page is posted back to the server for processing. PostBack is the name given to the process of submitting an ASP.NET page to the server for processing.
IsPostBack-This property is automatically set to False whenever a page is called for first time and whenever a server redirect a new instance of a page this property is set to True.
AutoPostBack-This property is by default set to False. So if we perform some action on control such as DropDownList, no events are performed because events are not recognized.