A type of home run that occurs when the bases are loaded and the batter with his home run brings in all the runners safely, including himself, scoring a total of four runs. This most often occurs when the batter hits the ball over the outfield fence for an automatic Grand Slam home run, which brings all runners home safely.
Sometimes referred to as a "Four-run Homer."
In any given year, there are usually around 120 Grand Slams hit. A rare type of Grand Slam is the In The Park Grand Slam that occurs when the batter hits the ball into the field and all three runners on base and the batter himself safely make it home scoring four runs. In total, there have only ever been 224 In The Park Grand Slams.
Grand Slam Home Run Records