A foul ball in softball is similar to that of baseball in that it is a legally batted ball that does not fall within the field of play. Except in cases where the batter already has two strikes on him or her, a foul ball that hits the ground results in a strike on the batter. If the batter hit a foul ball that hits the ground with two strikes in the count already, the count remains at two strikes.
A more specific definition of a foul ball is a ball that ends up in foul territory on either the first-base side or the third-base side of the diamond. If a player is able to catch the ball before it hits the ground or enters the grandstand, it results in an out call for the batter. This also goes for foul balls that go behind the home plate.