What is event bubbling in Flex?

What is event bubbling in Flex?

First, event bubbling is not specific to Flex, it's a feature related to AS3 event propagation.

Event propagation means the transference of a single event applying to multiple display objects. Each of those objects receives the event, instead of just the object in which the event originated.

I won't cover all the details of event propagation, google it for more info (http://www.adobe.com/devnet/actionscript/articles/event_handling_as3_03.html)

Event bubbling means an event dispatched from a display object will bubble up the display list, starting from the object dispatching the event to the stage.

Notice that you can also use the capture phase to listen to an event dispatched by one of a display object's children. See my comment here