The Open Position is a way of holding your partner, where both hands hold the other in front of you around hip height. The leader is on the bottom (open hands) and the follower is on top (a small U-form).
In salsa, the Open Position is most commonly used. It is used with many different hand holds that switch quickly. See Hand Holds.
Transitioning to Closed Position
Moving from Open Position to Closed Position can be done by the leader by letting go of the right hand, and moving it underneath her arm onto her back. Followers will understand this, but there is another smooth way to do this.
The leader can right hand, grab onto the wrist instead of hand, and make a rotating motion. See the video.
It is shown in the first few seconds of this video without explanations.