In baseball, when a batter hits the ball into play and successfully reaches first base, it is referred to as a single. This action occurs when the batter contacts the ball effectively and runs to the first base without being tagged out or forced out at the base. A single is significant because it allows the batter to get on base and potentially advance to subsequent bases during the play or on the next hit. Records in baseball often highlight players' single hits as they contribute to their overall batting average and importance within the game.