The BridgePattern decouples an abstraction?

I learned Bridge pattern from different articles and i have implemented that as per understanding . One thing that is confusing me is bridge pattern says

BridgePattern decouples an abstraction from its implementation so that the two can vary independently

what is mean by this statement? Is implementation resides at in separate jar ? what is mean by vary independently ? considering the provided link elaborate the answer.

http://ift.tt/1QJKbJw

Any help be greatly appreciated.