Thick Shots:
Fig. 1
Any shot between A and B will be a thick shot. As shown in the figure above, cue ball positions 1, 2, 3, and B are different positions with respect to a straight shot A. One can see there will be several shots in between A and B that will fall into a thick shot. White out portions in shot positions 1, 2, and 3 are just few examples of hidden or not seen part of the object ball with respect to a full hit or straight in shot.