STRIKE

Interesting reading from the 1876 rules of baseball defining the "strike zone"

"The batsman, on taking his position, must call for a 'high,' 'low,' or 'fair' pitch, and the umpire shall notify the pitcher to deliver the ball as required; such a call cannot be changed after the first pitch is delivered."
High - pitches over the plate between the batter's waist and shoulders
Low - pitches over the plate between the batter's waist and at least one foot from the ground.
Fair - pitches over the plate between the batter's shoulders and at least one foot from the ground.