A PostBack is any request for a page that is not the first request. A PostBack will always be in response to a user action (triggered most commonly by a Button, AutoPostBack control or Ajax).
Postback is the process of by which the browser sends information back to the server so that server can handle the event. The server executes the code sends the resulting HTML back to the browser again. Postback occurs only with web forms that have the runat="server" attribute.
A post back is round trip from the Browser to the server and then back to the browser. This enables you page to go through the asp engine on the server and any dynamic content to be updated.
Already executed