A cupped propeller means the blade trailing edges are formed into a curved shape.  In appearance, it looks as if the trailing edge was bent upwards into a small radius.  Trailing edge cup is incorporated into propeller designs to improve their efficiency when operated on higher speed boats and/or for propellers for turning at high RPM.  Typical use might be for example express cruisers with gasoline engines operating at speeds over 30 knots.  The propeller will be operating in a cavitating condition.  The trailing edge cup allows the cavitating propeller blade to generate more thrust, thus improving propeller efficiency.