In cricket, a run scored when the batsman has neither touched the ball with the bat, nor had the ball touch his body or clothing (which would make it a leg-bye), from a legitimate delivery by the bowler (i.e. not a wide or a no ball). As such it is deemed to be the fault of the wicket-keeper and the run is neither credited to the batsman or considered on the bowler's analysis, but just added to the batting team's total as an extra. The delivery counts as normal since the batsman could have hit the ball; no additional balls are bowled.
The umpire signals a bye to the scorers by holding his left hand straight up with the palm open.