This is a baseball phrase which refers to the area on the field where the pitcher pitches the ball from. It is typically a circle or oval shape and raised a specific distance off the ground. The distance from home plate and the height of the mound differ depending on the level of competition. Near the center of the mound is the pitcher's plate, or pitcher's rubber. The pitcher must be standing on the pitcher's plate when they begin their pitching motion.
In Major League Baseball, the pitcher's mound is 18 feet (5.5m) in diameter, with the pitcher's plate 18 inches (45.7cm) beyond the center of the mound. This places the pitcher's plate 60 feet 6 inches (18.4m) from the back of home plate. The mound may not be raised more than 10 inches (25.4cm) above home plate. The pitcher's mound is raised to allow the pitcher a pushing off point for their pitch; which adds velocity. Prior to a rule limiting the height of the mound, teams with an emphasis on pitching could take advantage by raising the height.