A home run, abbreviated HR, is a term in baseball for when the batter hits the ball and touches all the bases without an error being made by the team on defense. The most common way for a batter to hit a home run is to hit the ball over the outfield fence in fair territory. If the ball goes over the outfield fence but it is ruled a "foul ball", it does not count as a home run. Another way for a batter to hit a home run is to hit what is called an "inside-the-park" home run. If the batter touches all four bases after he hits the ball and it stays on the field, he scores a home run. This is an inside-the-park home run as long as no error is committed by the fielding team on the play.
In the early days of Major League Baseball, a home run was not awarded to a ball hit over the fence to win the game if the winning run scored before the batter-runner were to reach home plate to score. Therefore, what would otherwise be walk-off home runs were not commonplace, and players were often robbed of home runs. Due to this, for instance, Babe Ruth is not credited with a particular walk-off home run that would bring his career total to 715.