From Wikipedia (didn't feel like typing )
A poker run is an organized event using a motorcycle, boat, car or other form of transportation where participants travel over a predesignated route and, at designated stops on the route, draw playing card(s). The object is to have the best poker hand at the end of the run. Prizes (usually cash prizes) are awarded for the best hand; some runs will award smaller awards for lower hands. Poker runs usually require a fee to enter; part of the fee goes to funding the event (including the prizes), while the rest goes to the event's cause (usually a charity of some sort). Specific rules and details vary, depending on the event.