1. Short for dead ball shot.
2. A ball that has been used for some time, with a dirty surface, as opposed to a slick new (or highly polished used) ball. A spinning dead ball will transfer more spin to other balls it comes into contact with, and not be as fast on the cloth. Even cut shot angles may be affected because of the cling or skid (British: kick) effect, and professional players often ask a referee to clean a ball, mid-game. Others may actually be more used to dead balls and prefer them.