"Open" to the target means that your shoulders are angling away from the target, with your chest partially facing the target. "Closed" to the target means that your shoulders are perpendicular to the target. We are recommending that you try shooting with your shoulders in more of a closed position.
If you look at the first example on page 1 of Terry's form clock post, that person has his shoulders open to the target. The next example down, with the clock face superimposed, shows the shoulders perpendicular to the target.
If you study the clock face example, which shows good allignment, you will see that even with shoulders perpendicular to the target, there is still room to shoot the bow without string slap.
The string will be moving pretty close to the bow arm, however, and there might be string slap, for a variety of reasons, some controllable, some not. If you can learn to shoot with your shoulders perpendicular to the target, it will probably lead to better consistency. Some people, because of their body types or other reasons, prefer to shoot with their shoulders open to the target, and they can become good shots too, although it does add some additional variables that need to be controlled.
Masters of the Barebow III is another good DVD that covers some of these questions, and I would recommend that you view this DVD when you have an opportunity.