A foul ball is a hit baseball that lands in foul territory, outside the foul lines. Additionally, if the baseball is hit and initially bounces in fair territory between home plate and the bases, then bounces into foul territory before crossing a base, it is considered a foul ball.
A foul ball is considered a strike only under certain circumstances. If the batter has less than two strikes and hits a foul ball, it counts as a strike. If the batter has two strikes and hits a foul ball, it does not count as the third strike; it is considered a dead ball and the strike count remains the same.