A balls "Foot Print" usually refers to the amount of ball surface that is in contact with the lane.
The more of a balls surface that is in contact with the lane, the greater the influence the lane will have on that ball.
Larger footprints = more friction. More friction = more hook potential.
The hardness of the lane surface and the balls coverstock, affect how big the footprint is. The softer the materials, the larger the footprint will be on the lane.
The balls surface texture also affects the footprint size. The smoother the surface, the larger the footprint will be when the ball contacts the lane.