In listening to the tower at KORD during snowy days, the controller after giving landing clearance to an a/c always gives the pilots wind heading and strength, info on runway braking conditions, and a number for RDR. Now, I believe that RDR means 'Runway Distance Remaining', but in what way is it meant in this sort of exchange? If the controller says RDR 5000, does that mean that of a, say, 10000 ft runway, only 5000 feet have been plowed and are guaranteed to be passable? That is what I take it to mean, but thought some of the pilots out there might be able to clarify. Thanks!