Every wannabe should know this; definition of bounce by Golfsmith:
Bounce is an intentional design condition of the sole angle of an iron, measured in degrees, in which the trailing edge of the sole is below the leading edge(most often applied to sand wedges and high lob wedges). As a rule the greater the bounce angle , the more the clubhead can cut through tall grass and resist traveling too deeply into the sand.Wedges with less bounce are MORE EFFECTIVE for run-up shots,especially from normal turf or coarse sand.