What is the use of AutoPostBack ?

Answer:

AutoPostBack is a feature available that is available on few controls.
The main purpose of this feature is that, if there is any change done on the client side, then it should be handled on the server side.

Usage:

<asp:TextBox AutoPostBack="TRUE|FALSE" runat="server"/> 

Example:

<form runat="server">

<asp:TextBox id="txtBox1" runat="server" AutoPostBack="TRUE" />

</form>