Event statements

The way I’ve learned (and “learned” is stretching it a bit) to write an event listener is -

myButton.addEventListener(MouseEvent.CLICK, onClick);

function onClick(event:MouseEvent):void;
{

}

I keep seeing what seems to be the same thing written in the following way -

myButton.addEventListener(MouseEvent.CLICK,
function(evt:MouseEvent):void
{

}
);

Are these equivalent ways of doing the same thing and could “evt” be replaced by any name for your function?
If so, what’s the advantage of one over the other?