what is Event Bubbling

Event Bubbling is nothing but events raised by child controls as handled by the parent control.
Example: Suppose consider datagrid as parent control in which there are several child controls.There can be a column of link buttons right.Each link button has click event.Instead of writing event routine for each link button write one routine for parent which will handlde the click events of the child link button events.Parent can know which child actaully triggered the event.That thru arguments passed to event routine.

The ASP.NET page framework provides a technique called event bubbling that allows a child control to propagate events up its containment hierarchy. Event bubbling enables events to be raised from a more convenient location in the controls hierarchy and allows event handlers to be attached to the original control as well as to the control that exposes the bubbled event.

Event bubbling is used by the data-bound controls (Repeater, DataList, and DataGrid) to expose command events raised by child controls (within item templates) as top-level events. While ASP.NET server controls in the .NET Framework use event bubbling for command events (events whose event data class derives from CommandEventArgs), any event defined on a server control can be bubbled.
A control can participate in event bubbling through two methods that it inherits from the base class System.Web.UI.Control. These methods are OnBubbleEvent and RaiseBubbleEvent.

protected virtual bool OnBubbleEvent( object source, EventArgs args );
protected void RaiseBubbleEvent( object source, EventArgs args );