what is Autopostback in asp.net?

AutoPostBack is the mechanism , by which the page will be posted back to the server automatically based on some events in the web controls. In some of the web controls, the property called auto post back, which is set to true, will send the request to the server when an event happens in the control.

Example:-

TextBox has AutoPostBack property.

The AutoPostBack property is used to set or return whether or not an automatic post back occurs when user presses “ENTER” or “TAB” in the TextBox control.