What is PostBack in ASP.NET

Postback in simple terms is self referal of the page. In earlier version of ASP, the form would ‘POST’ values to another page for validation or some process using the post method.
But in ASP.NET, the page which accepts the values through its form would be responsible for validating/processing the values.
More @ http://www.codersource.net/asp_net_post_back.html